/*
 *  CFQ, or complete fairness queueing, disk scheduler.
 *
 *  Based on ideas from a previously unfinished io
 *  scheduler (round robin per-process disk scheduling) and Andrea Arcangeli.
 *
 *  Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
 */
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/blkdev.h>
#include <linux/elevator.h>
#include <linux/jiffies.h>
#include <linux/rbtree.h>
#include <linux/ioprio.h>
#include <linux/blktrace_api.h>
#include "cfq.h"

/*
 * tunables
 */
/* max queue in one round of service */
static const int cfq_quantum = 8;
static const int cfq_fifo_expire[2] = { HZ / 4, HZ / 8 };
/* maximum backwards seek, in KiB */
static const int cfq_back_max = 16 * 1024;
/* penalty of a backwards seek */
static const int cfq_back_penalty = 2;
static const int cfq_slice_sync = HZ / 10;
static int cfq_slice_async = HZ / 25;
static const int cfq_slice_async_rq = 2;
static int cfq_slice_idle = HZ / 125;
static int cfq_group_idle = HZ / 125;
static const int cfq_target_latency = HZ * 3/10; /* 300 ms */
static const int cfq_hist_divisor = 4;

/*
 * offset from end of service tree
 */
#define CFQ_IDLE_DELAY          (HZ / 5)

/*
 * below this threshold, we consider thinktime immediate
 */
#define CFQ_MIN_TT              (2)

#define CFQ_SLICE_SCALE         (5)
#define CFQ_HW_QUEUE_MIN        (5)
#define CFQ_SERVICE_SHIFT       12

#define CFQQ_SEEK_THR           (sector_t)(8 * 100)
#define CFQQ_CLOSE_THR          (sector_t)(8 * 1024)
#define CFQQ_SECT_THR_NONROT    (sector_t)(2 * 32)
#define CFQQ_SEEKY(cfqq)        (hweight32(cfqq->seek_history) > 32/8)

#define RQ_CIC(rq)              \
        ((struct cfq_io_context *) (rq)->elevator_private)
#define RQ_CFQQ(rq)             (struct cfq_queue *) ((rq)->elevator_private2)
#define RQ_CFQG(rq)             (struct cfq_group *) ((rq)->elevator_private3)

static struct kmem_cache *cfq_pool;
static struct kmem_cache *cfq_ioc_pool;

static DEFINE_PER_CPU(unsigned long, cfq_ioc_count);
static struct completion *ioc_gone;
static DEFINE_SPINLOCK(ioc_gone_lock);

static DEFINE_SPINLOCK(cic_index_lock);
static DEFINE_IDA(cic_index_ida);

#define CFQ_PRIO_LISTS          IOPRIO_BE_NR
#define cfq_class_idle(cfqq)    ((cfqq)->ioprio_class == IOPRIO_CLASS_IDLE)
#define cfq_class_rt(cfqq)      ((cfqq)->ioprio_class == IOPRIO_CLASS_RT)

#define sample_valid(samples)   ((samples) > 80)
#define rb_entry_cfqg(node)     rb_entry((node), struct cfq_group, rb_node)

/*
 * Most of our rbtree usage is for sorting with min extraction, so
 * if we cache the leftmost node we don't have to walk down the tree
 * to find it. Idea borrowed from Ingo Molnars CFS scheduler. We should
 * move this into the elevator for the rq sorting as well.
 */
struct cfq_rb_root {
        struct rb_root rb;
        struct rb_node *left;
        unsigned count;
        unsigned total_weight;
        u64 min_vdisktime;
};
#define CFQ_RB_ROOT     (struct cfq_rb_root) { .rb = RB_ROOT, .left = NULL, \
                        .count = 0, .min_vdisktime = 0, }

/*
 * Per process-grouping structure
 */
struct cfq_queue {
        /* reference count */
        int ref;
        /* various state flags, see below */
        unsigned int flags;
        /* parent cfq_data */
        struct cfq_data *cfqd;
        /* service_tree member */
        struct rb_node rb_node;
        /* service_tree key */
        unsigned long rb_key;
        /* prio tree member */
        struct rb_node p_node;
        /* prio tree root we belong to, if any */
        struct rb_root *p_root;
        /* sorted list of pending requests */
        struct rb_root sort_list;
        /* if fifo isn't expired, next request to serve */
        struct request *next_rq;
        /* requests queued in sort_list */
        int queued[2];
        /* currently allocated requests */
        int allocated[2];
        /* fifo list of requests in sort_list */
        struct list_head fifo;

        /* time when queue got scheduled in to dispatch first request. */
        unsigned long dispatch_start;
        unsigned int allocated_slice;
        unsigned int slice_dispatch;
        /* time when first request from queue completed and slice started. */
        unsigned long slice_start;
        unsigned long slice_end;
        long slice_resid;

        /* pending metadata requests */
        int meta_pending;
        /* number of requests that are on the dispatch list or inside driver */
        int dispatched;

        /* io prio of this group */
        unsigned short ioprio, org_ioprio;
        unsigned short ioprio_class, org_ioprio_class;

        pid_t pid;

        u32 seek_history;
        sector_t last_request_pos;

        struct cfq_rb_root *service_tree;
        struct cfq_queue *new_cfqq;
        struct cfq_group *cfqg;
        struct cfq_group *orig_cfqg;
        /* Number of sectors dispatched from queue in single dispatch round */
        unsigned long nr_sectors;
};

/*
 * First index in the service_trees.
 * IDLE is handled separately, so it has negative index
 */
enum wl_prio_t {
        BE_WORKLOAD = 0,
        RT_WORKLOAD = 1,
        IDLE_WORKLOAD = 2,
        CFQ_PRIO_NR,
};

/*
 * Second index in the service_trees.
 */
enum wl_type_t {
        ASYNC_WORKLOAD = 0,
        SYNC_NOIDLE_WORKLOAD = 1,
        SYNC_WORKLOAD = 2
};

/* This is per cgroup per device grouping structure */
struct cfq_group {
        /* group service_tree member */
        struct rb_node rb_node;

        /* group service_tree key */
        u64 vdisktime;
        unsigned int weight;

        /* number of cfqq currently on this group */
        int nr_cfqq;

        /*
         * Per group busy queus average. Useful for workload slice calc. We
         * create the array for each prio class but at run time it is used
         * only for RT and BE class and slot for IDLE class remains unused.
         * This is primarily done to avoid confusion and a gcc warning.
         */
        unsigned int busy_queues_avg[CFQ_PRIO_NR];
        /*
         * rr lists of queues with requests. We maintain service trees for
         * RT and BE classes. These trees are subdivided in subclasses
         * of SYNC, SYNC_NOIDLE and ASYNC based on workload type. For IDLE
         * class there is no subclassification and all the cfq queues go on
         * a single tree service_tree_idle.
         * Counts are embedded in the cfq_rb_root
         */
        struct cfq_rb_root service_trees[2][3];
        struct cfq_rb_root service_tree_idle;

        unsigned long saved_workload_slice;
        enum wl_type_t saved_workload;
        enum wl_prio_t saved_serving_prio;
        struct blkio_group blkg;
#ifdef CONFIG_CFQ_GROUP_IOSCHED
        struct hlist_node cfqd_node;
        int ref;
#endif
        /* number of requests that are on the dispatch list or inside driver */
        int dispatched;
};

/*
 * Per block device queue structure
 */
struct cfq_data {
        struct request_queue *queue;
        /* Root service tree for cfq_groups */
        struct cfq_rb_root grp_service_tree;
        struct cfq_group root_group;

        /*
         * The priority currently being served
         */
        enum wl_prio_t serving_prio;
        enum wl_type_t serving_type;
        unsigned long workload_expires;
        struct cfq_group *serving_group;

        /*
         * Each priority tree is sorted by next_request position.  These
         * trees are used when determining if two or more queues are
         * interleaving requests (see cfq_close_cooperator).
         */
        struct rb_root prio_trees[CFQ_PRIO_LISTS];

        unsigned int busy_queues;

        int rq_in_driver;
        int rq_in_flight[2];

        /*
         * queue-depth detection
         */
        int rq_queued;
        int hw_tag;
        /*
         * hw_tag can be
         * -1 => indeterminate, (cfq will behave as if NCQ is present, to allow better detection)
         *  1 => NCQ is present (hw_tag_est_depth is the estimated max depth)
         *  0 => no NCQ
         */
        int hw_tag_est_depth;
        unsigned int hw_tag_samples;

        /*
         * idle window management
         */
        struct timer_list idle_slice_timer;
        struct work_struct unplug_work;

        struct cfq_queue *active_queue;
        struct cfq_io_context *active_cic;

        /*
         * async queue for each priority case
         */
        struct cfq_queue *async_cfqq[2][IOPRIO_BE_NR];
        struct cfq_queue *async_idle_cfqq;

        sector_t last_position;

        /*
         * tunables, see top of file
         */
        unsigned int cfq_quantum;
        unsigned int cfq_fifo_expire[2];
        unsigned int cfq_back_penalty;
        unsigned int cfq_back_max;
        unsigned int cfq_slice[2];
        unsigned int cfq_slice_async_rq;
        unsigned int cfq_slice_idle;
        unsigned int cfq_group_idle;
        unsigned int cfq_latency;
        unsigned int cfq_group_isolation;

        unsigned int cic_index;
        struct list_head cic_list;

        /*
         * Fallback dummy cfqq for extreme OOM conditions
         */
        struct cfq_queue oom_cfqq;

        unsigned long last_delayed_sync;

        /* List of cfq groups being managed on this device*/
        struct hlist_head cfqg_list;
        struct rcu_head rcu;
};

static struct cfq_group *cfq_get_next_cfqg(struct cfq_data *cfqd);

static struct cfq_rb_root *service_tree_for(struct cfq_group *cfqg,
                                            enum wl_prio_t prio,
                                            enum wl_type_t type)
{
        if (!cfqg)
                return NULL;

        if (prio == IDLE_WORKLOAD)
                return &cfqg->service_tree_idle;

        return &cfqg->service_trees[prio][type];
}

enum cfqq_state_flags {
        CFQ_CFQQ_FLAG_on_rr = 0,        /* on round-robin busy list */
        CFQ_CFQQ_FLAG_wait_request,     /* waiting for a request */
        CFQ_CFQQ_FLAG_must_dispatch,    /* must be allowed a dispatch */
        CFQ_CFQQ_FLAG_must_alloc_slice, /* per-slice must_alloc flag */
        CFQ_CFQQ_FLAG_fifo_expire,      /* FIFO checked in this slice */
        CFQ_CFQQ_FLAG_idle_window,      /* slice idling enabled */
        CFQ_CFQQ_FLAG_prio_changed,     /* task priority has changed */
        CFQ_CFQQ_FLAG_slice_new,        /* no requests dispatched in slice */
        CFQ_CFQQ_FLAG_sync,             /* synchronous queue */
        CFQ_CFQQ_FLAG_coop,             /* cfqq is shared */
        CFQ_CFQQ_FLAG_split_coop,       /* shared cfqq will be splitted */
        CFQ_CFQQ_FLAG_deep,             /* sync cfqq experienced large depth */
        CFQ_CFQQ_FLAG_wait_busy,        /* Waiting for next request */
};

#define CFQ_CFQQ_FNS(name)                                              \
static inline void cfq_mark_cfqq_##name(struct cfq_queue *cfqq)         \
{                                                                       \
        (cfqq)->flags |= (1 << CFQ_CFQQ_FLAG_##name);                   \
}                                                                       \
static inline void cfq_clear_cfqq_##name(struct cfq_queue *cfqq)        \
{                                                                       \
        (cfqq)->flags &= ~(1 << CFQ_CFQQ_FLAG_##name);                  \
}                                                                       \
static inline int cfq_cfqq_##name(const struct cfq_queue *cfqq)         \
{                                                                       \
        return ((cfqq)->flags & (1 << CFQ_CFQQ_FLAG_##name)) != 0;      \
}

CFQ_CFQQ_FNS(on_rr);
CFQ_CFQQ_FNS(wait_request);
CFQ_CFQQ_FNS(must_dispatch);
CFQ_CFQQ_FNS(must_alloc_slice);
CFQ_CFQQ_FNS(fifo_expire);
CFQ_CFQQ_FNS(idle_window);
CFQ_CFQQ_FNS(prio_changed);
CFQ_CFQQ_FNS(slice_new);
CFQ_CFQQ_FNS(sync);
CFQ_CFQQ_FNS(coop);
CFQ_CFQQ_FNS(split_coop);
CFQ_CFQQ_FNS(deep);
CFQ_CFQQ_FNS(wait_busy);
#undef CFQ_CFQQ_FNS

#ifdef CONFIG_CFQ_GROUP_IOSCHED
#define cfq_log_cfqq(cfqd, cfqq, fmt, args...)  \
        blk_add_trace_msg((cfqd)->queue, "cfq%d%c %s " fmt, (cfqq)->pid, \
                        cfq_cfqq_sync((cfqq)) ? 'S' : 'A', \
                        blkg_path(&(cfqq)->cfqg->blkg), ##args);

#define cfq_log_cfqg(cfqd, cfqg, fmt, args...)                          \
        blk_add_trace_msg((cfqd)->queue, "%s " fmt,                     \
                                blkg_path(&(cfqg)->blkg), ##args);      \

#else
#define cfq_log_cfqq(cfqd, cfqq, fmt, args...)  \
        blk_add_trace_msg((cfqd)->queue, "cfq%d " fmt, (cfqq)->pid, ##args)
#define cfq_log_cfqg(cfqd, cfqg, fmt, args...)          do {} while (0);
#endif
#define cfq_log(cfqd, fmt, args...)     \
        blk_add_trace_msg((cfqd)->queue, "cfq " fmt, ##args)

/* Traverses through cfq group service trees */
#define for_each_cfqg_st(cfqg, i, j, st) \
        for (i = 0; i <= IDLE_WORKLOAD; i++) \
                for (j = 0, st = i < IDLE_WORKLOAD ? &cfqg->service_trees[i][j]\
                        : &cfqg->service_tree_idle; \
                        (i < IDLE_WORKLOAD && j <= SYNC_WORKLOAD) || \
                        (i == IDLE_WORKLOAD && j == 0); \
                        j++, st = i < IDLE_WORKLOAD ? \
                        &cfqg->service_trees[i][j]: NULL) \


static inline bool iops_mode(struct cfq_data *cfqd)
{
        /*
         * If we are not idling on queues and it is a NCQ drive, parallel
         * execution of requests is on and measuring time is not possible
         * in most of the cases until and unless we drive shallower queue
         * depths and that becomes a performance bottleneck. In such cases
         * switch to start providing fairness in terms of number of IOs.
         */
        if (!cfqd->cfq_slice_idle && cfqd->hw_tag)
                return true;
        else
                return false;
}

static inline enum wl_prio_t cfqq_prio(struct cfq_queue *cfqq)
{
        if (cfq_class_idle(cfqq))
                return IDLE_WORKLOAD;
        if (cfq_class_rt(cfqq))
                return RT_WORKLOAD;
        return BE_WORKLOAD;
}


static enum wl_type_t cfqq_type(struct cfq_queue *cfqq)
{
        if (!cfq_cfqq_sync(cfqq))
                return ASYNC_WORKLOAD;
        if (!cfq_cfqq_idle_window(cfqq))
                return SYNC_NOIDLE_WORKLOAD;
        return SYNC_WORKLOAD;
}

static inline int cfq_group_busy_queues_wl(enum wl_prio_t wl,
                                        struct cfq_data *cfqd,
                                        struct cfq_group *cfqg)
{
        if (wl == IDLE_WORKLOAD)
                return cfqg->service_tree_idle.count;

        return cfqg->service_trees[wl][ASYNC_WORKLOAD].count
                + cfqg->service_trees[wl][SYNC_NOIDLE_WORKLOAD].count
                + cfqg->service_trees[wl][SYNC_WORKLOAD].count;
}

static inline int cfqg_busy_async_queues(struct cfq_data *cfqd,
                                        struct cfq_group *cfqg)
{
        return cfqg->service_trees[RT_WORKLOAD][ASYNC_WORKLOAD].count
                + cfqg->service_trees[BE_WORKLOAD][ASYNC_WORKLOAD].count;
}

static void cfq_dispatch_insert(struct request_queue *, struct request *);
static struct cfq_queue *cfq_get_queue(struct cfq_data *, bool,
                                       struct io_context *, gfp_t);
static struct cfq_io_context *cfq_cic_lookup(struct cfq_data *,
                                                struct io_context *);

static inline struct cfq_queue *cic_to_cfqq(struct cfq_io_context *cic,
                                            bool is_sync)
{
        return cic->cfqq[is_sync];
}

static inline void cic_set_cfqq(struct cfq_io_context *cic,
                                struct cfq_queue *cfqq, bool is_sync)
{
        cic->cfqq[is_sync] = cfqq;
}

#define CIC_DEAD_KEY    1ul
#define CIC_DEAD_INDEX_SHIFT    1

static inline void *cfqd_dead_key(struct cfq_data *cfqd)
{
        return (void *)(cfqd->cic_index << CIC_DEAD_INDEX_SHIFT | CIC_DEAD_KEY);
}

static inline struct cfq_data *cic_to_cfqd(struct cfq_io_context *cic)
{
        struct cfq_data *cfqd = cic->key;

        if (unlikely((unsigned long) cfqd & CIC_DEAD_KEY))
                return NULL;

        return cfqd;
}

/*
 * We regard a request as SYNC, if it's either a read or has the SYNC bit
 * set (in which case it could also be direct WRITE).
 */
static inline bool cfq_bio_sync(struct bio *bio)
{
        return bio_data_dir(bio) == READ || (bio->bi_rw & REQ_SYNC);
}

/*
 * scheduler run of queue, if there are requests pending and no one in the
 * driver that will restart queueing
 */
static inline void cfq_schedule_dispatch(struct cfq_data *cfqd)
{
        if (cfqd->busy_queues) {
                cfq_log(cfqd, "schedule dispatch");
                kblockd_schedule_work(cfqd->queue, &cfqd->unplug_work);
        }
}

static int cfq_queue_empty(struct request_queue *q)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;

        return !cfqd->rq_queued;
}

/*
 * Scale schedule slice based on io priority. Use the sync time slice only
 * if a queue is marked sync and has sync io queued. A sync queue with async
 * io only, should not get full sync slice length.
 */
static inline int cfq_prio_slice(struct cfq_data *cfqd, bool sync,
                                 unsigned short prio)
{
        const int base_slice = cfqd->cfq_slice[sync];

        WARN_ON(prio >= IOPRIO_BE_NR);

        return base_slice + (base_slice/CFQ_SLICE_SCALE * (4 - prio));
}

static inline int
cfq_prio_to_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        return cfq_prio_slice(cfqd, cfq_cfqq_sync(cfqq), cfqq->ioprio);
}

static inline u64 cfq_scale_slice(unsigned long delta, struct cfq_group *cfqg)
{
        u64 d = delta << CFQ_SERVICE_SHIFT;

        d = d * BLKIO_WEIGHT_DEFAULT;
        do_div(d, cfqg->weight);
        return d;
}

static inline u64 max_vdisktime(u64 min_vdisktime, u64 vdisktime)
{
        s64 delta = (s64)(vdisktime - min_vdisktime);
        if (delta > 0)
                min_vdisktime = vdisktime;

        return min_vdisktime;
}

static inline u64 min_vdisktime(u64 min_vdisktime, u64 vdisktime)
{
        s64 delta = (s64)(vdisktime - min_vdisktime);
        if (delta < 0)
                min_vdisktime = vdisktime;

        return min_vdisktime;
}

static void update_min_vdisktime(struct cfq_rb_root *st)
{
        u64 vdisktime = st->min_vdisktime;
        struct cfq_group *cfqg;

        if (st->left) {
                cfqg = rb_entry_cfqg(st->left);
                vdisktime = min_vdisktime(vdisktime, cfqg->vdisktime);
        }

        st->min_vdisktime = max_vdisktime(st->min_vdisktime, vdisktime);
}

/*
 * get averaged number of queues of RT/BE priority.
 * average is updated, with a formula that gives more weight to higher numbers,
 * to quickly follows sudden increases and decrease slowly
 */

static inline unsigned cfq_group_get_avg_queues(struct cfq_data *cfqd,
                                        struct cfq_group *cfqg, bool rt)
{
        unsigned min_q, max_q;
        unsigned mult  = cfq_hist_divisor - 1;
        unsigned round = cfq_hist_divisor / 2;
        unsigned busy = cfq_group_busy_queues_wl(rt, cfqd, cfqg);

        min_q = min(cfqg->busy_queues_avg[rt], busy);
        max_q = max(cfqg->busy_queues_avg[rt], busy);
        cfqg->busy_queues_avg[rt] = (mult * max_q + min_q + round) /
                cfq_hist_divisor;
        return cfqg->busy_queues_avg[rt];
}

static inline unsigned
cfq_group_slice(struct cfq_data *cfqd, struct cfq_group *cfqg)
{
        struct cfq_rb_root *st = &cfqd->grp_service_tree;

        return cfq_target_latency * cfqg->weight / st->total_weight;
}

static inline unsigned
cfq_scaled_cfqq_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        unsigned slice = cfq_prio_to_slice(cfqd, cfqq);
        if (cfqd->cfq_latency) {
                /*
                 * interested queues (we consider only the ones with the same
                 * priority class in the cfq group)
                 */
                unsigned iq = cfq_group_get_avg_queues(cfqd, cfqq->cfqg,
                                                cfq_class_rt(cfqq));
                unsigned sync_slice = cfqd->cfq_slice[1];
                unsigned expect_latency = sync_slice * iq;
                unsigned group_slice = cfq_group_slice(cfqd, cfqq->cfqg);

                if (expect_latency > group_slice) {
                        unsigned base_low_slice = 2 * cfqd->cfq_slice_idle;
                        /* scale low_slice according to IO priority
                         * and sync vs async */
                        unsigned low_slice =
                                min(slice, base_low_slice * slice / sync_slice);
                        /* the adapted slice value is scaled to fit all iqs
                         * into the target latency */
                        slice = max(slice * group_slice / expect_latency,
                                    low_slice);
                }
        }
        return slice;
}

static inline void
cfq_set_prio_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        unsigned slice = cfq_scaled_cfqq_slice(cfqd, cfqq);

        cfqq->slice_start = jiffies;
        cfqq->slice_end = jiffies + slice;
        cfqq->allocated_slice = slice;
        cfq_log_cfqq(cfqd, cfqq, "set_slice=%lu", cfqq->slice_end - jiffies);
}

/*
 * We need to wrap this check in cfq_cfqq_slice_new(), since ->slice_end
 * isn't valid until the first request from the dispatch is activated
 * and the slice time set.
 */
static inline bool cfq_slice_used(struct cfq_queue *cfqq)
{
        if (cfq_cfqq_slice_new(cfqq))
                return false;
        if (time_before(jiffies, cfqq->slice_end))
                return false;

        return true;
}

/*
 * Lifted from AS - choose which of rq1 and rq2 that is best served now.
 * We choose the request that is closest to the head right now. Distance
 * behind the head is penalized and only allowed to a certain extent.
 */
static struct request *
cfq_choose_req(struct cfq_data *cfqd, struct request *rq1, struct request *rq2, sector_t last)
{
        sector_t s1, s2, d1 = 0, d2 = 0;
        unsigned long back_max;
#define CFQ_RQ1_WRAP    0x01 /* request 1 wraps */
#define CFQ_RQ2_WRAP    0x02 /* request 2 wraps */
        unsigned wrap = 0; /* bit mask: requests behind the disk head? */

        if (rq1 == NULL || rq1 == rq2)
                return rq2;
        if (rq2 == NULL)
                return rq1;

        if (rq_is_sync(rq1) && !rq_is_sync(rq2))
                return rq1;
        else if (rq_is_sync(rq2) && !rq_is_sync(rq1))
                return rq2;
        if ((rq1->cmd_flags & REQ_META) && !(rq2->cmd_flags & REQ_META))
                return rq1;
        else if ((rq2->cmd_flags & REQ_META) &&
                 !(rq1->cmd_flags & REQ_META))
                return rq2;

        s1 = blk_rq_pos(rq1);
        s2 = blk_rq_pos(rq2);

        /*
         * by definition, 1KiB is 2 sectors
         */
        back_max = cfqd->cfq_back_max * 2;

        /*
         * Strict one way elevator _except_ in the case where we allow
         * short backward seeks which are biased as twice the cost of a
         * similar forward seek.
         */
        if (s1 >= last)
                d1 = s1 - last;
        else if (s1 + back_max >= last)
                d1 = (last - s1) * cfqd->cfq_back_penalty;
        else
                wrap |= CFQ_RQ1_WRAP;

        if (s2 >= last)
                d2 = s2 - last;
        else if (s2 + back_max >= last)
                d2 = (last - s2) * cfqd->cfq_back_penalty;
        else
                wrap |= CFQ_RQ2_WRAP;

        /* Found required data */

        /*
         * By doing switch() on the bit mask "wrap" we avoid having to
         * check two variables for all permutations: --> faster!
         */
        switch (wrap) {
        case 0: /* common case for CFQ: rq1 and rq2 not wrapped */
                if (d1 < d2)
                        return rq1;
                else if (d2 < d1)
                        return rq2;
                else {
                        if (s1 >= s2)
                                return rq1;
                        else
                                return rq2;
                }

        case CFQ_RQ2_WRAP:
                return rq1;
        case CFQ_RQ1_WRAP:
                return rq2;
        case (CFQ_RQ1_WRAP|CFQ_RQ2_WRAP): /* both rqs wrapped */
        default:
                /*
                 * Since both rqs are wrapped,
                 * start with the one that's further behind head
                 * (--> only *one* back seek required),
                 * since back seek takes more time than forward.
                 */
                if (s1 <= s2)
                        return rq1;
                else
                        return rq2;
        }
}

/*
 * The below is leftmost cache rbtree addon
 */
static struct cfq_queue *cfq_rb_first(struct cfq_rb_root *root)
{
        /* Service tree is empty */
        if (!root->count)
                return NULL;

        if (!root->left)
                root->left = rb_first(&root->rb);

        if (root->left)
                return rb_entry(root->left, struct cfq_queue, rb_node);

        return NULL;
}

static struct cfq_group *cfq_rb_first_group(struct cfq_rb_root *root)
{
        if (!root->left)
                root->left = rb_first(&root->rb);

        if (root->left)
                return rb_entry_cfqg(root->left);

        return NULL;
}

static void rb_erase_init(struct rb_node *n, struct rb_root *root)
{
        rb_erase(n, root);
        RB_CLEAR_NODE(n);
}

static void cfq_rb_erase(struct rb_node *n, struct cfq_rb_root *root)
{
        if (root->left == n)
                root->left = NULL;
        rb_erase_init(n, &root->rb);
        --root->count;
}

/*
 * would be nice to take fifo expire time into account as well
 */
static struct request *
cfq_find_next_rq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                  struct request *last)
{
        struct rb_node *rbnext = rb_next(&last->rb_node);
        struct rb_node *rbprev = rb_prev(&last->rb_node);
        struct request *next = NULL, *prev = NULL;

        BUG_ON(RB_EMPTY_NODE(&last->rb_node));

        if (rbprev)
                prev = rb_entry_rq(rbprev);

        if (rbnext)
                next = rb_entry_rq(rbnext);
        else {
                rbnext = rb_first(&cfqq->sort_list);
                if (rbnext && rbnext != &last->rb_node)
                        next = rb_entry_rq(rbnext);
        }

        return cfq_choose_req(cfqd, next, prev, blk_rq_pos(last));
}

static unsigned long cfq_slice_offset(struct cfq_data *cfqd,
                                      struct cfq_queue *cfqq)
{
        /*
         * just an approximation, should be ok.
         */
        return (cfqq->cfqg->nr_cfqq - 1) * (cfq_prio_slice(cfqd, 1, 0) -
                       cfq_prio_slice(cfqd, cfq_cfqq_sync(cfqq), cfqq->ioprio));
}

static inline s64
cfqg_key(struct cfq_rb_root *st, struct cfq_group *cfqg)
{
        return cfqg->vdisktime - st->min_vdisktime;
}

static void
__cfq_group_service_tree_add(struct cfq_rb_root *st, struct cfq_group *cfqg)
{
        struct rb_node **node = &st->rb.rb_node;
        struct rb_node *parent = NULL;
        struct cfq_group *__cfqg;
        s64 key = cfqg_key(st, cfqg);
        int left = 1;

        while (*node != NULL) {
                parent = *node;
                __cfqg = rb_entry_cfqg(parent);

                if (key < cfqg_key(st, __cfqg))
                        node = &parent->rb_left;
                else {
                        node = &parent->rb_right;
                        left = 0;
                }
        }

        if (left)
                st->left = &cfqg->rb_node;

        rb_link_node(&cfqg->rb_node, parent, node);
        rb_insert_color(&cfqg->rb_node, &st->rb);
}

static void
cfq_group_service_tree_add(struct cfq_data *cfqd, struct cfq_group *cfqg)
{
        struct cfq_rb_root *st = &cfqd->grp_service_tree;
        struct cfq_group *__cfqg;
        struct rb_node *n;

        cfqg->nr_cfqq++;
        if (!RB_EMPTY_NODE(&cfqg->rb_node))
                return;

        /*
         * Currently put the group at the end. Later implement something
         * so that groups get lesser vtime based on their weights, so that
         * if group does not loose all if it was not continously backlogged.
         */
        n = rb_last(&st->rb);
        if (n) {
                __cfqg = rb_entry_cfqg(n);
                cfqg->vdisktime = __cfqg->vdisktime + CFQ_IDLE_DELAY;
        } else
                cfqg->vdisktime = st->min_vdisktime;

        __cfq_group_service_tree_add(st, cfqg);
        st->total_weight += cfqg->weight;
}

static void
cfq_group_service_tree_del(struct cfq_data *cfqd, struct cfq_group *cfqg)
{
        struct cfq_rb_root *st = &cfqd->grp_service_tree;

        BUG_ON(cfqg->nr_cfqq < 1);
        cfqg->nr_cfqq--;

        /* If there are other cfq queues under this group, don't delete it */
        if (cfqg->nr_cfqq)
                return;

        cfq_log_cfqg(cfqd, cfqg, "del_from_rr group");
        st->total_weight -= cfqg->weight;
        if (!RB_EMPTY_NODE(&cfqg->rb_node))
                cfq_rb_erase(&cfqg->rb_node, st);
        cfqg->saved_workload_slice = 0;
        cfq_blkiocg_update_dequeue_stats(&cfqg->blkg, 1);
}

static inline unsigned int cfq_cfqq_slice_usage(struct cfq_queue *cfqq)
{
        unsigned int slice_used;

        /*
         * Queue got expired before even a single request completed or
         * got expired immediately after first request completion.
         */
        if (!cfqq->slice_start || cfqq->slice_start == jiffies) {
                /*
                 * Also charge the seek time incurred to the group, otherwise
                 * if there are mutiple queues in the group, each can dispatch
                 * a single request on seeky media and cause lots of seek time
                 * and group will never know it.
                 */
                slice_used = max_t(unsigned, (jiffies - cfqq->dispatch_start),
                                        1);
        } else {
                slice_used = jiffies - cfqq->slice_start;
                if (slice_used > cfqq->allocated_slice)
                        slice_used = cfqq->allocated_slice;
        }

        return slice_used;
}

static void cfq_group_served(struct cfq_data *cfqd, struct cfq_group *cfqg,
                                struct cfq_queue *cfqq)
{
        struct cfq_rb_root *st = &cfqd->grp_service_tree;
        unsigned int used_sl, charge;
        int nr_sync = cfqg->nr_cfqq - cfqg_busy_async_queues(cfqd, cfqg)
                        - cfqg->service_tree_idle.count;

        BUG_ON(nr_sync < 0);
        used_sl = charge = cfq_cfqq_slice_usage(cfqq);

        if (iops_mode(cfqd))
                charge = cfqq->slice_dispatch;
        else if (!cfq_cfqq_sync(cfqq) && !nr_sync)
                charge = cfqq->allocated_slice;

        /* Can't update vdisktime while group is on service tree */
        cfq_rb_erase(&cfqg->rb_node, st);
        cfqg->vdisktime += cfq_scale_slice(charge, cfqg);
        __cfq_group_service_tree_add(st, cfqg);

        /* This group is being expired. Save the context */
        if (time_after(cfqd->workload_expires, jiffies)) {
                cfqg->saved_workload_slice = cfqd->workload_expires
                                                - jiffies;
                cfqg->saved_workload = cfqd->serving_type;
                cfqg->saved_serving_prio = cfqd->serving_prio;
        } else
                cfqg->saved_workload_slice = 0;

        cfq_log_cfqg(cfqd, cfqg, "served: vt=%llu min_vt=%llu", cfqg->vdisktime,
                                        st->min_vdisktime);
        cfq_log_cfqq(cfqq->cfqd, cfqq, "sl_used=%u disp=%u charge=%u iops=%u"
                        " sect=%u", used_sl, cfqq->slice_dispatch, charge,
                        iops_mode(cfqd), cfqq->nr_sectors);
        cfq_blkiocg_update_timeslice_used(&cfqg->blkg, used_sl);
        cfq_blkiocg_set_start_empty_time(&cfqg->blkg);
}

#ifdef CONFIG_CFQ_GROUP_IOSCHED
static inline struct cfq_group *cfqg_of_blkg(struct blkio_group *blkg)
{
        if (blkg)
                return container_of(blkg, struct cfq_group, blkg);
        return NULL;
}

void cfq_update_blkio_group_weight(void *key, struct blkio_group *blkg,
                                        unsigned int weight)
{
        cfqg_of_blkg(blkg)->weight = weight;
}

static struct cfq_group *
cfq_find_alloc_cfqg(struct cfq_data *cfqd, struct cgroup *cgroup, int create)
{
        struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgroup);
        struct cfq_group *cfqg = NULL;
        void *key = cfqd;
        int i, j;
        struct cfq_rb_root *st;
        struct backing_dev_info *bdi = &cfqd->queue->backing_dev_info;
        unsigned int major, minor;

        cfqg = cfqg_of_blkg(blkiocg_lookup_group(blkcg, key));
        if (cfqg && !cfqg->blkg.dev && bdi->dev && dev_name(bdi->dev)) {
                sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
                cfqg->blkg.dev = MKDEV(major, minor);
                goto done;
        }
        if (cfqg || !create)
                goto done;

        cfqg = kzalloc_node(sizeof(*cfqg), GFP_ATOMIC, cfqd->queue->node);
        if (!cfqg)
                goto done;

        for_each_cfqg_st(cfqg, i, j, st)
                *st = CFQ_RB_ROOT;
        RB_CLEAR_NODE(&cfqg->rb_node);

        /*
         * Take the initial reference that will be released on destroy
         * This can be thought of a joint reference by cgroup and
         * elevator which will be dropped by either elevator exit
         * or cgroup deletion path depending on who is exiting first.
         */
        cfqg->ref = 1;

        /*
         * Add group onto cgroup list. It might happen that bdi->dev is
         * not initialized yet. Initialize this new group without major
         * and minor info and this info will be filled in once a new thread
         * comes for IO. See code above.
         */
        if (bdi->dev) {
                sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
                cfq_blkiocg_add_blkio_group(blkcg, &cfqg->blkg, (void *)cfqd,
                                        MKDEV(major, minor));
        } else
                cfq_blkiocg_add_blkio_group(blkcg, &cfqg->blkg, (void *)cfqd,
                                        0);

        cfqg->weight = blkcg_get_weight(blkcg, cfqg->blkg.dev);

        /* Add group on cfqd list */
        hlist_add_head(&cfqg->cfqd_node, &cfqd->cfqg_list);

done:
        return cfqg;
}

/*
 * Search for the cfq group current task belongs to. If create = 1, then also
 * create the cfq group if it does not exist. request_queue lock must be held.
 */
static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd, int create)
{
        struct cgroup *cgroup;
        struct cfq_group *cfqg = NULL;

        rcu_read_lock();
        cgroup = task_cgroup(current, blkio_subsys_id);
        cfqg = cfq_find_alloc_cfqg(cfqd, cgroup, create);
        if (!cfqg && create)
                cfqg = &cfqd->root_group;
        rcu_read_unlock();
        return cfqg;
}

static inline struct cfq_group *cfq_ref_get_cfqg(struct cfq_group *cfqg)
{
        cfqg->ref++;
        return cfqg;
}

static void cfq_link_cfqq_cfqg(struct cfq_queue *cfqq, struct cfq_group *cfqg)
{
        /* Currently, all async queues are mapped to root group */
        if (!cfq_cfqq_sync(cfqq))
                cfqg = &cfqq->cfqd->root_group;

        cfqq->cfqg = cfqg;
        /* cfqq reference on cfqg */
        cfqq->cfqg->ref++;
}

static void cfq_put_cfqg(struct cfq_group *cfqg)
{
        struct cfq_rb_root *st;
        int i, j;

        BUG_ON(cfqg->ref <= 0);
        cfqg->ref--;
        if (cfqg->ref)
                return;
        for_each_cfqg_st(cfqg, i, j, st)
                BUG_ON(!RB_EMPTY_ROOT(&st->rb));
        kfree(cfqg);
}

static void cfq_destroy_cfqg(struct cfq_data *cfqd, struct cfq_group *cfqg)
{
        /* Something wrong if we are trying to remove same group twice */
        BUG_ON(hlist_unhashed(&cfqg->cfqd_node));

        hlist_del_init(&cfqg->cfqd_node);

        /*
         * Put the reference taken at the time of creation so that when all
         * queues are gone, group can be destroyed.
         */
        cfq_put_cfqg(cfqg);
}

static void cfq_release_cfq_groups(struct cfq_data *cfqd)
{
        struct hlist_node *pos, *n;
        struct cfq_group *cfqg;

        hlist_for_each_entry_safe(cfqg, pos, n, &cfqd->cfqg_list, cfqd_node) {
                /*
                 * If cgroup removal path got to blk_group first and removed
                 * it from cgroup list, then it will take care of destroying
                 * cfqg also.
                 */
                if (!cfq_blkiocg_del_blkio_group(&cfqg->blkg))
                        cfq_destroy_cfqg(cfqd, cfqg);
        }
}

/*
 * Blk cgroup controller notification saying that blkio_group object is being
 * delinked as associated cgroup object is going away. That also means that
 * no new IO will come in this group. So get rid of this group as soon as
 * any pending IO in the group is finished.
 *
 * This function is called under rcu_read_lock(). key is the rcu protected
 * pointer. That means "key" is a valid cfq_data pointer as long as we are rcu
 * read lock.
 *
 * "key" was fetched from blkio_group under blkio_cgroup->lock. That means
 * it should not be NULL as even if elevator was exiting, cgroup deltion
 * path got to it first.
 */
void cfq_unlink_blkio_group(void *key, struct blkio_group *blkg)
{
        unsigned long  flags;
        struct cfq_data *cfqd = key;

        spin_lock_irqsave(cfqd->queue->queue_lock, flags);
        cfq_destroy_cfqg(cfqd, cfqg_of_blkg(blkg));
        spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
}

#else /* GROUP_IOSCHED */
static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd, int create)
{
        return &cfqd->root_group;
}

static inline struct cfq_group *cfq_ref_get_cfqg(struct cfq_group *cfqg)
{
        return cfqg;
}

static inline void
cfq_link_cfqq_cfqg(struct cfq_queue *cfqq, struct cfq_group *cfqg) {
        cfqq->cfqg = cfqg;
}

static void cfq_release_cfq_groups(struct cfq_data *cfqd) {}
static inline void cfq_put_cfqg(struct cfq_group *cfqg) {}

#endif /* GROUP_IOSCHED */

/*
 * The cfqd->service_trees holds all pending cfq_queue's that have
 * requests waiting to be processed. It is sorted in the order that
 * we will service the queues.
 */
static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                                 bool add_front)
{
        struct rb_node **p, *parent;
        struct cfq_queue *__cfqq;
        unsigned long rb_key;
        struct cfq_rb_root *service_tree;
        int left;
        int new_cfqq = 1;
        int group_changed = 0;

#ifdef CONFIG_CFQ_GROUP_IOSCHED
        if (!cfqd->cfq_group_isolation
            && cfqq_type(cfqq) == SYNC_NOIDLE_WORKLOAD
            && cfqq->cfqg && cfqq->cfqg != &cfqd->root_group) {
                /* Move this cfq to root group */
                cfq_log_cfqq(cfqd, cfqq, "moving to root group");
                if (!RB_EMPTY_NODE(&cfqq->rb_node))
                        cfq_group_service_tree_del(cfqd, cfqq->cfqg);
                cfqq->orig_cfqg = cfqq->cfqg;
                cfqq->cfqg = &cfqd->root_group;
                cfqd->root_group.ref++;
                group_changed = 1;
        } else if (!cfqd->cfq_group_isolation
                   && cfqq_type(cfqq) == SYNC_WORKLOAD && cfqq->orig_cfqg) {
                /* cfqq is sequential now needs to go to its original group */
                BUG_ON(cfqq->cfqg != &cfqd->root_group);
                if (!RB_EMPTY_NODE(&cfqq->rb_node))
                        cfq_group_service_tree_del(cfqd, cfqq->cfqg);
                cfq_put_cfqg(cfqq->cfqg);
                cfqq->cfqg = cfqq->orig_cfqg;
                cfqq->orig_cfqg = NULL;
                group_changed = 1;
                cfq_log_cfqq(cfqd, cfqq, "moved to origin group");
        }
#endif

        service_tree = service_tree_for(cfqq->cfqg, cfqq_prio(cfqq),
                                                cfqq_type(cfqq));
        if (cfq_class_idle(cfqq)) {
                rb_key = CFQ_IDLE_DELAY;
                parent = rb_last(&service_tree->rb);
                if (parent && parent != &cfqq->rb_node) {
                        __cfqq = rb_entry(parent, struct cfq_queue, rb_node);
                        rb_key += __cfqq->rb_key;
                } else
                        rb_key += jiffies;
        } else if (!add_front) {
                /*
                 * Get our rb key offset. Subtract any residual slice
                 * value carried from last service. A negative resid
                 * count indicates slice overrun, and this should position
                 * the next service time further away in the tree.
                 */
                rb_key = cfq_slice_offset(cfqd, cfqq) + jiffies;
                rb_key -= cfqq->slice_resid;
                cfqq->slice_resid = 0;
        } else {
                rb_key = -HZ;
                __cfqq = cfq_rb_first(service_tree);
                rb_key += __cfqq ? __cfqq->rb_key : jiffies;
        }

        if (!RB_EMPTY_NODE(&cfqq->rb_node)) {
                new_cfqq = 0;
                /*
                 * same position, nothing more to do
                 */
                if (rb_key == cfqq->rb_key &&
                    cfqq->service_tree == service_tree)
                        return;

                cfq_rb_erase(&cfqq->rb_node, cfqq->service_tree);
                cfqq->service_tree = NULL;
        }

        left = 1;
        parent = NULL;
        cfqq->service_tree = service_tree;
        p = &service_tree->rb.rb_node;
        while (*p) {
                struct rb_node **n;

                parent = *p;
                __cfqq = rb_entry(parent, struct cfq_queue, rb_node);

                /*
                 * sort by key, that represents service time.
                 */
                if (time_before(rb_key, __cfqq->rb_key))
                        n = &(*p)->rb_left;
                else {
                        n = &(*p)->rb_right;
                        left = 0;
                }

                p = n;
        }

        if (left)
                service_tree->left = &cfqq->rb_node;

        cfqq->rb_key = rb_key;
        rb_link_node(&cfqq->rb_node, parent, p);
        rb_insert_color(&cfqq->rb_node, &service_tree->rb);
        service_tree->count++;
        if ((add_front || !new_cfqq) && !group_changed)
                return;
        cfq_group_service_tree_add(cfqd, cfqq->cfqg);
}

static struct cfq_queue *
cfq_prio_tree_lookup(struct cfq_data *cfqd, struct rb_root *root,
                     sector_t sector, struct rb_node **ret_parent,
                     struct rb_node ***rb_link)
{
        struct rb_node **p, *parent;
        struct cfq_queue *cfqq = NULL;

        parent = NULL;
        p = &root->rb_node;
        while (*p) {
                struct rb_node **n;

                parent = *p;
                cfqq = rb_entry(parent, struct cfq_queue, p_node);

                /*
                 * Sort strictly based on sector.  Smallest to the left,
                 * largest to the right.
                 */
                if (sector > blk_rq_pos(cfqq->next_rq))
                        n = &(*p)->rb_right;
                else if (sector < blk_rq_pos(cfqq->next_rq))
                        n = &(*p)->rb_left;
                else
                        break;
                p = n;
                cfqq = NULL;
        }

        *ret_parent = parent;
        if (rb_link)
                *rb_link = p;
        return cfqq;
}

static void cfq_prio_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        struct rb_node **p, *parent;
        struct cfq_queue *__cfqq;

        if (cfqq->p_root) {
                rb_erase(&cfqq->p_node, cfqq->p_root);
                cfqq->p_root = NULL;
        }

        if (cfq_class_idle(cfqq))
                return;
        if (!cfqq->next_rq)
                return;

        cfqq->p_root = &cfqd->prio_trees[cfqq->org_ioprio];
        __cfqq = cfq_prio_tree_lookup(cfqd, cfqq->p_root,
                                      blk_rq_pos(cfqq->next_rq), &parent, &p);
        if (!__cfqq) {
                rb_link_node(&cfqq->p_node, parent, p);
                rb_insert_color(&cfqq->p_node, cfqq->p_root);
        } else
                cfqq->p_root = NULL;
}

/*
 * Update cfqq's position in the service tree.
 */
static void cfq_resort_rr_list(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        /*
         * Resorting requires the cfqq to be on the RR list already.
         */
        if (cfq_cfqq_on_rr(cfqq)) {
                cfq_service_tree_add(cfqd, cfqq, 0);
                cfq_prio_tree_add(cfqd, cfqq);
        }
}

/*
 * add to busy list of queues for service, trying to be fair in ordering
 * the pending list according to last request service
 */
static void cfq_add_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        cfq_log_cfqq(cfqd, cfqq, "add_to_rr");
        BUG_ON(cfq_cfqq_on_rr(cfqq));
        cfq_mark_cfqq_on_rr(cfqq);
        cfqd->busy_queues++;

        cfq_resort_rr_list(cfqd, cfqq);
}

/*
 * Called when the cfqq no longer has requests pending, remove it from
 * the service tree.
 */
static void cfq_del_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        cfq_log_cfqq(cfqd, cfqq, "del_from_rr");
        BUG_ON(!cfq_cfqq_on_rr(cfqq));
        cfq_clear_cfqq_on_rr(cfqq);

        if (!RB_EMPTY_NODE(&cfqq->rb_node)) {
                cfq_rb_erase(&cfqq->rb_node, cfqq->service_tree);
                cfqq->service_tree = NULL;
        }
        if (cfqq->p_root) {
                rb_erase(&cfqq->p_node, cfqq->p_root);
                cfqq->p_root = NULL;
        }

        cfq_group_service_tree_del(cfqd, cfqq->cfqg);
        BUG_ON(!cfqd->busy_queues);
        cfqd->busy_queues--;
}

/*
 * rb tree support functions
 */
static void cfq_del_rq_rb(struct request *rq)
{
        struct cfq_queue *cfqq = RQ_CFQQ(rq);
        const int sync = rq_is_sync(rq);

        BUG_ON(!cfqq->queued[sync]);
        cfqq->queued[sync]--;

        elv_rb_del(&cfqq->sort_list, rq);

        if (cfq_cfqq_on_rr(cfqq) && RB_EMPTY_ROOT(&cfqq->sort_list)) {
                /*
                 * Queue will be deleted from service tree when we actually
                 * expire it later. Right now just remove it from prio tree
                 * as it is empty.
                 */
                if (cfqq->p_root) {
                        rb_erase(&cfqq->p_node, cfqq->p_root);
                        cfqq->p_root = NULL;
                }
        }
}

static void cfq_add_rq_rb(struct request *rq)
{
        struct cfq_queue *cfqq = RQ_CFQQ(rq);
        struct cfq_data *cfqd = cfqq->cfqd;
        struct request *__alias, *prev;

        cfqq->queued[rq_is_sync(rq)]++;

        /*
         * looks a little odd, but the first insert might return an alias.
         * if that happens, put the alias on the dispatch list
         */
        while ((__alias = elv_rb_add(&cfqq->sort_list, rq)) != NULL)
                cfq_dispatch_insert(cfqd->queue, __alias);

        if (!cfq_cfqq_on_rr(cfqq))
                cfq_add_cfqq_rr(cfqd, cfqq);

        /*
         * check if this request is a better next-serve candidate
         */
        prev = cfqq->next_rq;
        cfqq->next_rq = cfq_choose_req(cfqd, cfqq->next_rq, rq, cfqd->last_position);

        /*
         * adjust priority tree position, if ->next_rq changes
         */
        if (prev != cfqq->next_rq)
                cfq_prio_tree_add(cfqd, cfqq);

        BUG_ON(!cfqq->next_rq);
}

static void cfq_reposition_rq_rb(struct cfq_queue *cfqq, struct request *rq)
{
        elv_rb_del(&cfqq->sort_list, rq);
        cfqq->queued[rq_is_sync(rq)]--;
        cfq_blkiocg_update_io_remove_stats(&(RQ_CFQG(rq))->blkg,
                                        rq_data_dir(rq), rq_is_sync(rq));
        cfq_add_rq_rb(rq);
        cfq_blkiocg_update_io_add_stats(&(RQ_CFQG(rq))->blkg,
                        &cfqq->cfqd->serving_group->blkg, rq_data_dir(rq),
                        rq_is_sync(rq));
}

static struct request *
cfq_find_rq_fmerge(struct cfq_data *cfqd, struct bio *bio)
{
        struct task_struct *tsk = current;
        struct cfq_io_context *cic;
        struct cfq_queue *cfqq;

        cic = cfq_cic_lookup(cfqd, tsk->io_context);
        if (!cic)
                return NULL;

        cfqq = cic_to_cfqq(cic, cfq_bio_sync(bio));
        if (cfqq) {
                sector_t sector = bio->bi_sector + bio_sectors(bio);

                return elv_rb_find(&cfqq->sort_list, sector);
        }

        return NULL;
}

static void cfq_activate_request(struct request_queue *q, struct request *rq)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;

        cfqd->rq_in_driver++;
        cfq_log_cfqq(cfqd, RQ_CFQQ(rq), "activate rq, drv=%d",
                                                cfqd->rq_in_driver);

        cfqd->last_position = blk_rq_pos(rq) + blk_rq_sectors(rq);
}

static void cfq_deactivate_request(struct request_queue *q, struct request *rq)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;

        WARN_ON(!cfqd->rq_in_driver);
        cfqd->rq_in_driver--;
        cfq_log_cfqq(cfqd, RQ_CFQQ(rq), "deactivate rq, drv=%d",
                                                cfqd->rq_in_driver);
}

static void cfq_remove_request(struct request *rq)
{
        struct cfq_queue *cfqq = RQ_CFQQ(rq);

        if (cfqq->next_rq == rq)
                cfqq->next_rq = cfq_find_next_rq(cfqq->cfqd, cfqq, rq);

        list_del_init(&rq->queuelist);
        cfq_del_rq_rb(rq);

        cfqq->cfqd->rq_queued--;
        cfq_blkiocg_update_io_remove_stats(&(RQ_CFQG(rq))->blkg,
                                        rq_data_dir(rq), rq_is_sync(rq));
        if (rq->cmd_flags & REQ_META) {
                WARN_ON(!cfqq->meta_pending);
                cfqq->meta_pending--;
        }
}

static int cfq_merge(struct request_queue *q, struct request **req,
                     struct bio *bio)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct request *__rq;

        __rq = cfq_find_rq_fmerge(cfqd, bio);
        if (__rq && elv_rq_merge_ok(__rq, bio)) {
                *req = __rq;
                return ELEVATOR_FRONT_MERGE;
        }

        return ELEVATOR_NO_MERGE;
}

static void cfq_merged_request(struct request_queue *q, struct request *req,
                               int type)
{
        if (type == ELEVATOR_FRONT_MERGE) {
                struct cfq_queue *cfqq = RQ_CFQQ(req);

                cfq_reposition_rq_rb(cfqq, req);
        }
}

static void cfq_bio_merged(struct request_queue *q, struct request *req,
                                struct bio *bio)
{
        cfq_blkiocg_update_io_merged_stats(&(RQ_CFQG(req))->blkg,
                                        bio_data_dir(bio), cfq_bio_sync(bio));
}

static void
cfq_merged_requests(struct request_queue *q, struct request *rq,
                    struct request *next)
{
        struct cfq_queue *cfqq = RQ_CFQQ(rq);
        /*
         * reposition in fifo if next is older than rq
         */
        if (!list_empty(&rq->queuelist) && !list_empty(&next->queuelist) &&
            time_before(rq_fifo_time(next), rq_fifo_time(rq))) {
                list_move(&rq->queuelist, &next->queuelist);
                rq_set_fifo_time(rq, rq_fifo_time(next));
        }

        if (cfqq->next_rq == next)
                cfqq->next_rq = rq;
        cfq_remove_request(next);
        cfq_blkiocg_update_io_merged_stats(&(RQ_CFQG(rq))->blkg,
                                        rq_data_dir(next), rq_is_sync(next));
}

static int cfq_allow_merge(struct request_queue *q, struct request *rq,
                           struct bio *bio)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct cfq_io_context *cic;
        struct cfq_queue *cfqq;

        /*
         * Disallow merge of a sync bio into an async request.
         */
        if (cfq_bio_sync(bio) && !rq_is_sync(rq))
                return false;

        /*
         * Lookup the cfqq that this bio will be queued with. Allow
         * merge only if rq is queued there.
         */
        cic = cfq_cic_lookup(cfqd, current->io_context);
        if (!cic)
                return false;

        cfqq = cic_to_cfqq(cic, cfq_bio_sync(bio));
        return cfqq == RQ_CFQQ(rq);
}

static inline void cfq_del_timer(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        del_timer(&cfqd->idle_slice_timer);
        cfq_blkiocg_update_idle_time_stats(&cfqq->cfqg->blkg);
}

static void __cfq_set_active_queue(struct cfq_data *cfqd,
                                   struct cfq_queue *cfqq)
{
        if (cfqq) {
                cfq_log_cfqq(cfqd, cfqq, "set_active wl_prio:%d wl_type:%d",
                                cfqd->serving_prio, cfqd->serving_type);
                cfq_blkiocg_update_avg_queue_size_stats(&cfqq->cfqg->blkg);
                cfqq->slice_start = 0;
                cfqq->dispatch_start = jiffies;
                cfqq->allocated_slice = 0;
                cfqq->slice_end = 0;
                cfqq->slice_dispatch = 0;
                cfqq->nr_sectors = 0;

                cfq_clear_cfqq_wait_request(cfqq);
                cfq_clear_cfqq_must_dispatch(cfqq);
                cfq_clear_cfqq_must_alloc_slice(cfqq);
                cfq_clear_cfqq_fifo_expire(cfqq);
                cfq_mark_cfqq_slice_new(cfqq);

                cfq_del_timer(cfqd, cfqq);
        }

        cfqd->active_queue = cfqq;
}

/*
 * current cfqq expired its slice (or was too idle), select new one
 */
static void
__cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                    bool timed_out)
{
        cfq_log_cfqq(cfqd, cfqq, "slice expired t=%d", timed_out);

        if (cfq_cfqq_wait_request(cfqq))
                cfq_del_timer(cfqd, cfqq);

        cfq_clear_cfqq_wait_request(cfqq);
        cfq_clear_cfqq_wait_busy(cfqq);

        /*
         * If this cfqq is shared between multiple processes, check to
         * make sure that those processes are still issuing I/Os within
         * the mean seek distance.  If not, it may be time to break the
         * queues apart again.
         */
        if (cfq_cfqq_coop(cfqq) && CFQQ_SEEKY(cfqq))
                cfq_mark_cfqq_split_coop(cfqq);

        /*
         * store what was left of this slice, if the queue idled/timed out
         */
        if (timed_out) {
                if (cfq_cfqq_slice_new(cfqq))
                        cfqq->slice_resid = cfq_scaled_cfqq_slice(cfqd, cfqq);
                else
                        cfqq->slice_resid = cfqq->slice_end - jiffies;
                cfq_log_cfqq(cfqd, cfqq, "resid=%ld", cfqq->slice_resid);
        }

        cfq_group_served(cfqd, cfqq->cfqg, cfqq);

        if (cfq_cfqq_on_rr(cfqq) && RB_EMPTY_ROOT(&cfqq->sort_list))
                cfq_del_cfqq_rr(cfqd, cfqq);

        cfq_resort_rr_list(cfqd, cfqq);

        if (cfqq == cfqd->active_queue)
                cfqd->active_queue = NULL;

        if (cfqd->active_cic) {
                put_io_context(cfqd->active_cic->ioc);
                cfqd->active_cic = NULL;
        }
}

static inline void cfq_slice_expired(struct cfq_data *cfqd, bool timed_out)
{
        struct cfq_queue *cfqq = cfqd->active_queue;

        if (cfqq)
                __cfq_slice_expired(cfqd, cfqq, timed_out);
}

/*
 * Get next queue for service. Unless we have a queue preemption,
 * we'll simply select the first cfqq in the service tree.
 */
static struct cfq_queue *cfq_get_next_queue(struct cfq_data *cfqd)
{
        struct cfq_rb_root *service_tree =
                service_tree_for(cfqd->serving_group, cfqd->serving_prio,
                                        cfqd->serving_type);

        if (!cfqd->rq_queued)
                return NULL;

        /* There is nothing to dispatch */
        if (!service_tree)
                return NULL;
        if (RB_EMPTY_ROOT(&service_tree->rb))
                return NULL;
        return cfq_rb_first(service_tree);
}

static struct cfq_queue *cfq_get_next_queue_forced(struct cfq_data *cfqd)
{
        struct cfq_group *cfqg;
        struct cfq_queue *cfqq;
        int i, j;
        struct cfq_rb_root *st;

        if (!cfqd->rq_queued)
                return NULL;

        cfqg = cfq_get_next_cfqg(cfqd);
        if (!cfqg)
                return NULL;

        for_each_cfqg_st(cfqg, i, j, st)
                if ((cfqq = cfq_rb_first(st)) != NULL)
                        return cfqq;
        return NULL;
}

/*
 * Get and set a new active queue for service.
 */
static struct cfq_queue *cfq_set_active_queue(struct cfq_data *cfqd,
                                              struct cfq_queue *cfqq)
{
        if (!cfqq)
                cfqq = cfq_get_next_queue(cfqd);

        __cfq_set_active_queue(cfqd, cfqq);
        return cfqq;
}

static inline sector_t cfq_dist_from_last(struct cfq_data *cfqd,
                                          struct request *rq)
{
        if (blk_rq_pos(rq) >= cfqd->last_position)
                return blk_rq_pos(rq) - cfqd->last_position;
        else
                return cfqd->last_position - blk_rq_pos(rq);
}

static inline int cfq_rq_close(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                               struct request *rq)
{
        return cfq_dist_from_last(cfqd, rq) <= CFQQ_CLOSE_THR;
}

static struct cfq_queue *cfqq_close(struct cfq_data *cfqd,
                                    struct cfq_queue *cur_cfqq)
{
        struct rb_root *root = &cfqd->prio_trees[cur_cfqq->org_ioprio];
        struct rb_node *parent, *node;
        struct cfq_queue *__cfqq;
        sector_t sector = cfqd->last_position;

        if (RB_EMPTY_ROOT(root))
                return NULL;

        /*
         * First, if we find a request starting at the end of the last
         * request, choose it.
         */
        __cfqq = cfq_prio_tree_lookup(cfqd, root, sector, &parent, NULL);
        if (__cfqq)
                return __cfqq;

        /*
         * If the exact sector wasn't found, the parent of the NULL leaf
         * will contain the closest sector.
         */
        __cfqq = rb_entry(parent, struct cfq_queue, p_node);
        if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq))
                return __cfqq;

        if (blk_rq_pos(__cfqq->next_rq) < sector)
                node = rb_next(&__cfqq->p_node);
        else
                node = rb_prev(&__cfqq->p_node);
        if (!node)
                return NULL;

        __cfqq = rb_entry(node, struct cfq_queue, p_node);
        if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq))
                return __cfqq;

        return NULL;
}

/*
 * cfqd - obvious
 * cur_cfqq - passed in so that we don't decide that the current queue is
 *            closely cooperating with itself.
 *
 * So, basically we're assuming that that cur_cfqq has dispatched at least
 * one request, and that cfqd->last_position reflects a position on the disk
 * associated with the I/O issued by cur_cfqq.  I'm not sure this is a valid
 * assumption.
 */
static struct cfq_queue *cfq_close_cooperator(struct cfq_data *cfqd,
                                              struct cfq_queue *cur_cfqq)
{
        struct cfq_queue *cfqq;

        if (cfq_class_idle(cur_cfqq))
                return NULL;
        if (!cfq_cfqq_sync(cur_cfqq))
                return NULL;
        if (CFQQ_SEEKY(cur_cfqq))
                return NULL;

        /*
         * Don't search priority tree if it's the only queue in the group.
         */
        if (cur_cfqq->cfqg->nr_cfqq == 1)
                return NULL;

        /*
         * We should notice if some of the queues are cooperating, eg
         * working closely on the same area of the disk. In that case,
         * we can group them together and don't waste time idling.
         */
        cfqq = cfqq_close(cfqd, cur_cfqq);
        if (!cfqq)
                return NULL;

        /* If new queue belongs to different cfq_group, don't choose it */
        if (cur_cfqq->cfqg != cfqq->cfqg)
                return NULL;

        /*
         * It only makes sense to merge sync queues.
         */
        if (!cfq_cfqq_sync(cfqq))
                return NULL;
        if (CFQQ_SEEKY(cfqq))
                return NULL;

        /*
         * Do not merge queues of different priority classes
         */
        if (cfq_class_rt(cfqq) != cfq_class_rt(cur_cfqq))
                return NULL;

        return cfqq;
}

/*
 * Determine whether we should enforce idle window for this queue.
 */

static bool cfq_should_idle(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        enum wl_prio_t prio = cfqq_prio(cfqq);
        struct cfq_rb_root *service_tree = cfqq->service_tree;

        BUG_ON(!service_tree);
        BUG_ON(!service_tree->count);

        if (!cfqd->cfq_slice_idle)
                return false;

        /* We never do for idle class queues. */
        if (prio == IDLE_WORKLOAD)
                return false;

        /* We do for queues that were marked with idle window flag. */
        if (cfq_cfqq_idle_window(cfqq) &&
           !(blk_queue_nonrot(cfqd->queue) && cfqd->hw_tag))
                return true;

        /*
         * Otherwise, we do only if they are the last ones
         * in their service tree.
         */
        if (service_tree->count == 1 && cfq_cfqq_sync(cfqq))
                return true;
        cfq_log_cfqq(cfqd, cfqq, "Not idling. st->count:%d",
                        service_tree->count);
        return false;
}

static void cfq_arm_slice_timer(struct cfq_data *cfqd)
{
        struct cfq_queue *cfqq = cfqd->active_queue;
        struct cfq_io_context *cic;
        unsigned long sl, group_idle = 0;

        /*
         * SSD device without seek penalty, disable idling. But only do so
         * for devices that support queuing, otherwise we still have a problem
         * with sync vs async workloads.
         */
        if (blk_queue_nonrot(cfqd->queue) && cfqd->hw_tag)
                return;

        WARN_ON(!RB_EMPTY_ROOT(&cfqq->sort_list));
        WARN_ON(cfq_cfqq_slice_new(cfqq));

        /*
         * idle is disabled, either manually or by past process history
         */
        if (!cfq_should_idle(cfqd, cfqq)) {
                /* no queue idling. Check for group idling */
                if (cfqd->cfq_group_idle)
                        group_idle = cfqd->cfq_group_idle;
                else
                        return;
        }

        /*
         * still active requests from this queue, don't idle
         */
        if (cfqq->dispatched)
                return;

        /*
         * task has exited, don't wait
         */
        cic = cfqd->active_cic;
        if (!cic || !atomic_read(&cic->ioc->nr_tasks))
                return;

        /*
         * If our average think time is larger than the remaining time
         * slice, then don't idle. This avoids overrunning the allotted
         * time slice.
         */
        if (sample_valid(cic->ttime_samples) &&
            (cfqq->slice_end - jiffies < cic->ttime_mean)) {
                cfq_log_cfqq(cfqd, cfqq, "Not idling. think_time:%d",
                                cic->ttime_mean);
                return;
        }

        /* There are other queues in the group, don't do group idle */
        if (group_idle && cfqq->cfqg->nr_cfqq > 1)
                return;

        cfq_mark_cfqq_wait_request(cfqq);

        if (group_idle)
                sl = cfqd->cfq_group_idle;
        else
                sl = cfqd->cfq_slice_idle;

        mod_timer(&cfqd->idle_slice_timer, jiffies + sl);
        cfq_blkiocg_update_set_idle_time_stats(&cfqq->cfqg->blkg);
        cfq_log_cfqq(cfqd, cfqq, "arm_idle: %lu group_idle: %d", sl,
                        group_idle ? 1 : 0);
}

/*
 * Move request from internal lists to the request queue dispatch list.
 */
static void cfq_dispatch_insert(struct request_queue *q, struct request *rq)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct cfq_queue *cfqq = RQ_CFQQ(rq);

        cfq_log_cfqq(cfqd, cfqq, "dispatch_insert");

        cfqq->next_rq = cfq_find_next_rq(cfqd, cfqq, rq);
        cfq_remove_request(rq);
        cfqq->dispatched++;
        (RQ_CFQG(rq))->dispatched++;
        elv_dispatch_sort(q, rq);

        cfqd->rq_in_flight[cfq_cfqq_sync(cfqq)]++;
        cfqq->nr_sectors += blk_rq_sectors(rq);
        cfq_blkiocg_update_dispatch_stats(&cfqq->cfqg->blkg, blk_rq_bytes(rq),
                                        rq_data_dir(rq), rq_is_sync(rq));
}

/*
 * return expired entry, or NULL to just start from scratch in rbtree

 */
static struct request *cfq_check_fifo(struct cfq_queue *cfqq)
{
        struct request *rq = NULL;

        if (cfq_cfqq_fifo_expire(cfqq))
                return NULL;

        cfq_mark_cfqq_fifo_expire(cfqq);

        if (list_empty(&cfqq->fifo))
                return NULL;

        rq = rq_entry_fifo(cfqq->fifo.next);
        if (time_before(jiffies, rq_fifo_time(rq)))
                rq = NULL;

        cfq_log_cfqq(cfqq->cfqd, cfqq, "fifo=%p", rq);
        return rq;
}

static inline int
cfq_prio_to_maxrq(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        const int base_rq = cfqd->cfq_slice_async_rq;

        WARN_ON(cfqq->ioprio >= IOPRIO_BE_NR);

        return 2 * (base_rq + base_rq * (CFQ_PRIO_LISTS - 1 - cfqq->ioprio));
}

/*
 * Must be called with the queue_lock held.
 */
static int cfqq_process_refs(struct cfq_queue *cfqq)
{
        int process_refs, io_refs;

        io_refs = cfqq->allocated[READ] + cfqq->allocated[WRITE];
        process_refs = cfqq->ref - io_refs;
        BUG_ON(process_refs < 0);
        return process_refs;
}

static void cfq_setup_merge(struct cfq_queue *cfqq, struct cfq_queue *new_cfqq)
{
        int process_refs, new_process_refs;
        struct cfq_queue *__cfqq;

        /*
         * If there are no process references on the new_cfqq, then it is
         * unsafe to follow the ->new_cfqq chain as other cfqq's in the
         * chain may have dropped their last reference (not just their
         * last process reference).
         */
        if (!cfqq_process_refs(new_cfqq))
                return;

        /* Avoid a circular list and skip interim queue merges */
        while ((__cfqq = new_cfqq->new_cfqq)) {
                if (__cfqq == cfqq)
                        return;
                new_cfqq = __cfqq;
        }

        process_refs = cfqq_process_refs(cfqq);
        new_process_refs = cfqq_process_refs(new_cfqq);
        /*
         * If the process for the cfqq has gone away, there is no
         * sense in merging the queues.
         */
        if (process_refs == 0 || new_process_refs == 0)
                return;

        /*
         * Merge in the direction of the lesser amount of work.
         */
        if (new_process_refs >= process_refs) {
                cfqq->new_cfqq = new_cfqq;
                new_cfqq->ref += process_refs;
        } else {
                new_cfqq->new_cfqq = cfqq;
                cfqq->ref += new_process_refs;
        }
}

static enum wl_type_t cfq_choose_wl(struct cfq_data *cfqd,
                                struct cfq_group *cfqg, enum wl_prio_t prio)
{
        struct cfq_queue *queue;
        int i;
        bool key_valid = false;
        unsigned long lowest_key = 0;
        enum wl_type_t cur_best = SYNC_NOIDLE_WORKLOAD;

        for (i = 0; i <= SYNC_WORKLOAD; ++i) {
                /* select the one with lowest rb_key */
                queue = cfq_rb_first(service_tree_for(cfqg, prio, i));
                if (queue &&
                    (!key_valid || time_before(queue->rb_key, lowest_key))) {
                        lowest_key = queue->rb_key;
                        cur_best = i;
                        key_valid = true;
                }
        }

        return cur_best;
}

static void choose_service_tree(struct cfq_data *cfqd, struct cfq_group *cfqg)
{
        unsigned slice;
        unsigned count;
        struct cfq_rb_root *st;
        unsigned group_slice;
        enum wl_prio_t original_prio = cfqd->serving_prio;

        /* Choose next priority. RT > BE > IDLE */
        if (cfq_group_busy_queues_wl(RT_WORKLOAD, cfqd, cfqg))
                cfqd->serving_prio = RT_WORKLOAD;
        else if (cfq_group_busy_queues_wl(BE_WORKLOAD, cfqd, cfqg))
                cfqd->serving_prio = BE_WORKLOAD;
        else {
                cfqd->serving_prio = IDLE_WORKLOAD;
                cfqd->workload_expires = jiffies + 1;
                return;
        }

        if (original_prio != cfqd->serving_prio)
                goto new_workload;

        /*
         * For RT and BE, we have to choose also the type
         * (SYNC, SYNC_NOIDLE, ASYNC), and to compute a workload
         * expiration time
         */
        st = service_tree_for(cfqg, cfqd->serving_prio, cfqd->serving_type);
        count = st->count;

        /*
         * check workload expiration, and that we still have other queues ready
         */
        if (count && !time_after(jiffies, cfqd->workload_expires))
                return;

new_workload:
        /* otherwise select new workload type */
        cfqd->serving_type =
                cfq_choose_wl(cfqd, cfqg, cfqd->serving_prio);
        st = service_tree_for(cfqg, cfqd->serving_prio, cfqd->serving_type);
        count = st->count;

        /*
         * the workload slice is computed as a fraction of target latency
         * proportional to the number of queues in that workload, over
         * all the queues in the same priority class
         */
        group_slice = cfq_group_slice(cfqd, cfqg);

        slice = group_slice * count /
                max_t(unsigned, cfqg->busy_queues_avg[cfqd->serving_prio],
                      cfq_group_busy_queues_wl(cfqd->serving_prio, cfqd, cfqg));

        if (cfqd->serving_type == ASYNC_WORKLOAD) {
                unsigned int tmp;

                /*
                 * Async queues are currently system wide. Just taking
                 * proportion of queues with-in same group will lead to higher
                 * async ratio system wide as generally root group is going
                 * to have higher weight. A more accurate thing would be to
                 * calculate system wide asnc/sync ratio.
                 */
                tmp = cfq_target_latency * cfqg_busy_async_queues(cfqd, cfqg);
                tmp = tmp/cfqd->busy_queues;
                slice = min_t(unsigned, slice, tmp);

                /* async workload slice is scaled down according to
                 * the sync/async slice ratio. */
                slice = slice * cfqd->cfq_slice[0] / cfqd->cfq_slice[1];
        } else
                /* sync workload slice is at least 2 * cfq_slice_idle */
                slice = max(slice, 2 * cfqd->cfq_slice_idle);

        slice = max_t(unsigned, slice, CFQ_MIN_TT);
        cfq_log(cfqd, "workload slice:%d", slice);
        cfqd->workload_expires = jiffies + slice;
}

static struct cfq_group *cfq_get_next_cfqg(struct cfq_data *cfqd)
{
        struct cfq_rb_root *st = &cfqd->grp_service_tree;
        struct cfq_group *cfqg;

        if (RB_EMPTY_ROOT(&st->rb))
                return NULL;
        cfqg = cfq_rb_first_group(st);
        update_min_vdisktime(st);
        return cfqg;
}

static void cfq_choose_cfqg(struct cfq_data *cfqd)
{
        struct cfq_group *cfqg = cfq_get_next_cfqg(cfqd);

        cfqd->serving_group = cfqg;

        /* Restore the workload type data */
        if (cfqg->saved_workload_slice) {
                cfqd->workload_expires = jiffies + cfqg->saved_workload_slice;
                cfqd->serving_type = cfqg->saved_workload;
                cfqd->serving_prio = cfqg->saved_serving_prio;
        } else
                cfqd->workload_expires = jiffies - 1;

        choose_service_tree(cfqd, cfqg);
}

/*
 * Select a queue for service. If we have a current active queue,
 * check whether to continue servicing it, or retrieve and set a new one.
 */
static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)
{
        struct cfq_queue *cfqq, *new_cfqq = NULL;

        cfqq = cfqd->active_queue;
        if (!cfqq)
                goto new_queue;

        if (!cfqd->rq_queued)
                return NULL;

        /*
         * We were waiting for group to get backlogged. Expire the queue
         */
        if (cfq_cfqq_wait_busy(cfqq) && !RB_EMPTY_ROOT(&cfqq->sort_list))
                goto expire;

        /*
         * The active queue has run out of time, expire it and select new.
         */
        if (cfq_slice_used(cfqq) && !cfq_cfqq_must_dispatch(cfqq)) {
                /*
                 * If slice had not expired at the completion of last request
                 * we might not have turned on wait_busy flag. Don't expire
                 * the queue yet. Allow the group to get backlogged.
                 *
                 * The very fact that we have used the slice, that means we
                 * have been idling all along on this queue and it should be
                 * ok to wait for this request to complete.
                 */
                if (cfqq->cfqg->nr_cfqq == 1 && RB_EMPTY_ROOT(&cfqq->sort_list)
                    && cfqq->dispatched && cfq_should_idle(cfqd, cfqq)) {
                        cfqq = NULL;
                        goto keep_queue;
                } else
                        goto check_group_idle;
        }

        /*
         * The active queue has requests and isn't expired, allow it to
         * dispatch.
         */
        if (!RB_EMPTY_ROOT(&cfqq->sort_list))
                goto keep_queue;

        /*
         * If another queue has a request waiting within our mean seek
         * distance, let it run.  The expire code will check for close
         * cooperators and put the close queue at the front of the service
         * tree.  If possible, merge the expiring queue with the new cfqq.
         */
        new_cfqq = cfq_close_cooperator(cfqd, cfqq);
        if (new_cfqq) {
                if (!cfqq->new_cfqq)
                        cfq_setup_merge(cfqq, new_cfqq);
                goto expire;
        }

        /*
         * No requests pending. If the active queue still has requests in
         * flight or is idling for a new request, allow either of these
         * conditions to happen (or time out) before selecting a new queue.
         */
        if (timer_pending(&cfqd->idle_slice_timer)) {
                cfqq = NULL;
                goto keep_queue;
        }

        /*
         * This is a deep seek queue, but the device is much faster than
         * the queue can deliver, don't idle
         **/
        if (CFQQ_SEEKY(cfqq) && cfq_cfqq_idle_window(cfqq) &&
            (cfq_cfqq_slice_new(cfqq) ||
            (cfqq->slice_end - jiffies > jiffies - cfqq->slice_start))) {
                cfq_clear_cfqq_deep(cfqq);
                cfq_clear_cfqq_idle_window(cfqq);
        }

        if (cfqq->dispatched && cfq_should_idle(cfqd, cfqq)) {
                cfqq = NULL;
                goto keep_queue;
        }

        /*
         * If group idle is enabled and there are requests dispatched from
         * this group, wait for requests to complete.
         */
check_group_idle:
        if (cfqd->cfq_group_idle && cfqq->cfqg->nr_cfqq == 1
            && cfqq->cfqg->dispatched) {
                cfqq = NULL;
                goto keep_queue;
        }

expire:
        cfq_slice_expired(cfqd, 0);
new_queue:
        /*
         * Current queue expired. Check if we have to switch to a new
         * service tree
         */
        if (!new_cfqq)
                cfq_choose_cfqg(cfqd);

        cfqq = cfq_set_active_queue(cfqd, new_cfqq);
keep_queue:
        return cfqq;
}

static int __cfq_forced_dispatch_cfqq(struct cfq_queue *cfqq)
{
        int dispatched = 0;

        while (cfqq->next_rq) {
                cfq_dispatch_insert(cfqq->cfqd->queue, cfqq->next_rq);
                dispatched++;
        }

        BUG_ON(!list_empty(&cfqq->fifo));

        /* By default cfqq is not expired if it is empty. Do it explicitly */
        __cfq_slice_expired(cfqq->cfqd, cfqq, 0);
        return dispatched;
}

/*
 * Drain our current requests. Used for barriers and when switching
 * io schedulers on-the-fly.
 */
static int cfq_forced_dispatch(struct cfq_data *cfqd)
{
        struct cfq_queue *cfqq;
        int dispatched = 0;

        /* Expire the timeslice of the current active queue first */
        cfq_slice_expired(cfqd, 0);
        while ((cfqq = cfq_get_next_queue_forced(cfqd)) != NULL) {
                __cfq_set_active_queue(cfqd, cfqq);
                dispatched += __cfq_forced_dispatch_cfqq(cfqq);
        }

        BUG_ON(cfqd->busy_queues);

        cfq_log(cfqd, "forced_dispatch=%d", dispatched);
        return dispatched;
}

static inline bool cfq_slice_used_soon(struct cfq_data *cfqd,
        struct cfq_queue *cfqq)
{
        /* the queue hasn't finished any request, can't estimate */
        if (cfq_cfqq_slice_new(cfqq))
                return true;
        if (time_after(jiffies + cfqd->cfq_slice_idle * cfqq->dispatched,
                cfqq->slice_end))
                return true;

        return false;
}

static bool cfq_may_dispatch(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        unsigned int max_dispatch;

        /*
         * Drain async requests before we start sync IO
         */
        if (cfq_should_idle(cfqd, cfqq) && cfqd->rq_in_flight[BLK_RW_ASYNC])
                return false;

        /*
         * If this is an async queue and we have sync IO in flight, let it wait
         */
        if (cfqd->rq_in_flight[BLK_RW_SYNC] && !cfq_cfqq_sync(cfqq))
                return false;

        max_dispatch = max_t(unsigned int, cfqd->cfq_quantum / 2, 1);
        if (cfq_class_idle(cfqq))
                max_dispatch = 1;

        /*
         * Does this cfqq already have too much IO in flight?
         */
        if (cfqq->dispatched >= max_dispatch) {
                /*
                 * idle queue must always only have a single IO in flight
                 */
                if (cfq_class_idle(cfqq))
                        return false;

                /*
                 * We have other queues, don't allow more IO from this one
                 */
                if (cfqd->busy_queues > 1 && cfq_slice_used_soon(cfqd, cfqq))
                        return false;

                /*
                 * Sole queue user, no limit
                 */
                if (cfqd->busy_queues == 1)
                        max_dispatch = -1;
                else
                        /*
                         * Normally we start throttling cfqq when cfq_quantum/2
                         * requests have been dispatched. But we can drive
                         * deeper queue depths at the beginning of slice
                         * subjected to upper limit of cfq_quantum.
                         * */
                        max_dispatch = cfqd->cfq_quantum;
        }

        /*
         * Async queues must wait a bit before being allowed dispatch.
         * We also ramp up the dispatch depth gradually for async IO,
         * based on the last sync IO we serviced
         */
        if (!cfq_cfqq_sync(cfqq) && cfqd->cfq_latency) {
                unsigned long last_sync = jiffies - cfqd->last_delayed_sync;
                unsigned int depth;

                depth = last_sync / cfqd->cfq_slice[1];
                if (!depth && !cfqq->dispatched)
                        depth = 1;
                if (depth < max_dispatch)
                        max_dispatch = depth;
        }

        /*
         * If we're below the current max, allow a dispatch
         */
        return cfqq->dispatched < max_dispatch;
}

/*
 * Dispatch a request from cfqq, moving them to the request queue
 * dispatch list.
 */
static bool cfq_dispatch_request(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        struct request *rq;

        BUG_ON(RB_EMPTY_ROOT(&cfqq->sort_list));

        if (!cfq_may_dispatch(cfqd, cfqq))
                return false;

        /*
         * follow expired path, else get first next available
         */
        rq = cfq_check_fifo(cfqq);
        if (!rq)
                rq = cfqq->next_rq;

        /*
         * insert request into driver dispatch list
         */
        cfq_dispatch_insert(cfqd->queue, rq);

        if (!cfqd->active_cic) {
                struct cfq_io_context *cic = RQ_CIC(rq);

                atomic_long_inc(&cic->ioc->refcount);
                cfqd->active_cic = cic;
        }

        return true;
}

/*
 * Find the cfqq that we need to service and move a request from that to the
 * dispatch list
 */
static int cfq_dispatch_requests(struct request_queue *q, int force)
{
        struct cfq_data *cfqd = q->elevator->elevator_data;
        struct cfq_queue *cfqq;

        if (!cfqd->busy_queues)
                return 0;

        if (unlikely(force))
                return cfq_forced_dispatch(cfqd);

        cfqq = cfq_select_queue(cfqd);
        if (!cfqq)
                return 0;

        /*
         * Dispatch a request from this cfqq, if it is allowed
         */
        if (!cfq_dispatch_request(cfqd, cfqq))
                return 0;

        cfqq->slice_dispatch++;
        cfq_clear_cfqq_must_dispatch(cfqq);

        /*
         * expire an async queue immediately if it has used up its slice. idle
         * queue always expire after 1 dispatch round.
         */
        if (cfqd->busy_queues > 1 && ((!cfq_cfqq_sync(cfqq) &&
            cfqq->slice_dispatch >= cfq_prio_to_maxrq(cfqd, cfqq)) ||
            cfq_class_idle(cfqq))) {
                cfqq->slice_end = jiffies + 1;
                cfq_slice_expired(cfqd, 0);
        }

        cfq_log_cfqq(cfqd, cfqq, "dispatched a request");
        return 1;
}

/*
 * task holds one reference to the queue, dropped when task exits. each rq
 * in-flight on this queue also holds a reference, dropped when rq is freed.
 *
 * Each cfq queue took a reference on the parent group. Drop it now.
 * queue lock must be held here.
 */
static void cfq_put_queue(struct cfq_queue *cfqq)
{
        struct cfq_data *cfqd = cfqq->cfqd;
        struct cfq_group *cfqg, *orig_cfqg;

        BUG_ON(cfqq->ref <= 0);

        cfqq->ref--;
        if (cfqq->ref)
                return;

        cfq_log_cfqq(cfqd, cfqq, "put_queue");
        BUG_ON(rb_first(&cfqq->sort_list));
        BUG_ON(cfqq->allocated[READ] + cfqq->allocated[WRITE]);
        cfqg = cfqq->cfqg;
        orig_cfqg = cfqq->orig_cfqg;

        if (unlikely(cfqd->active_queue == cfqq)) {
                __cfq_slice_expired(cfqd, cfqq, 0);
                cfq_schedule_dispatch(cfqd);
        }

        BUG_ON(cfq_cfqq_on_rr(cfqq));
        kmem_cache_free(cfq_pool, cfqq);
        cfq_put_cfqg(cfqg);
        if (orig_cfqg)
                cfq_put_cfqg(orig_cfqg);
}

/*
 * Must always be called with the rcu_read_lock() held
 */
static void
__call_for_each_cic(struct io_context *ioc,
                    void (*func)(struct io_context *, struct cfq_io_context *))
{
        struct cfq_io_context *cic;
        struct hlist_node *n;

        hlist_for_each_entry_rcu(cic, n, &ioc->cic_list, cic_list)
                func(ioc, cic);
}

/*
 * Call func for each cic attached to this ioc.
 */
static void
call_for_each_cic(struct io_context *ioc,
                  void (*func)(struct io_context *, struct cfq_io_context *))
{
        rcu_read_lock();
        __call_for_each_cic(ioc, func);
        rcu_read_unlock();
}

static void cfq_cic_free_rcu(struct rcu_head *head)
{
        struct cfq_io_context *cic;

        cic = container_of(head, struct cfq_io_context, rcu_head);

        kmem_cache_free(cfq_ioc_pool, cic);
        elv_ioc_count_dec(cfq_ioc_count);

        if (ioc_gone) {
                /*
                 * CFQ scheduler is exiting, grab exit lock and check
                 * the pending io context count. If it hits zero,
                 * complete ioc_gone and set it back to NULL
                 */
                spin_lock(&ioc_gone_lock);
                if (ioc_gone && !elv_ioc_count_read(cfq_ioc_count)) {
                        complete(ioc_gone);
                        ioc_gone = NULL;
                }
                spin_unlock(&ioc_gone_lock);
        }
}

static void cfq_cic_free(struct cfq_io_context *cic)
{
        call_rcu(&cic->rcu_head, cfq_cic_free_rcu);
}

static void cic_free_func(struct io_context *ioc, struct cfq_io_context *cic)
{
        unsigned long flags;
        unsigned long dead_key = (unsigned long) cic->key;

        BUG_ON(!(dead_key & CIC_DEAD_KEY));

        spin_lock_irqsave(&ioc->lock, flags);
        radix_tree_delete(&ioc->radix_root, dead_key >> CIC_DEAD_INDEX_SHIFT);
        hlist_del_rcu(&cic->cic_list);
        spin_unlock_irqrestore(&ioc->lock, flags);

        cfq_cic_free(cic);
}

/*
 * Must be called with rcu_read_lock() held or preemption otherwise disabled.
 * Only two callers of this - ->dtor() which is called with the rcu_read_lock(),
 * and ->trim() which is called with the task lock held
 */
static void cfq_free_io_context(struct io_context *ioc)
{
        /*
         * ioc->refcount is zero here, or we are called from elv_unregister(),
         * so no more cic's are allowed to be linked into this ioc.  So it
         * should be ok to iterate over the known list, we will see all cic's
         * since no new ones are added.
         */
        __call_for_each_cic(ioc, cic_free_func);
}

static void cfq_put_cooperator(struct cfq_queue *cfqq)
{
        struct cfq_queue *__cfqq, *next;

        /*
         * If this queue was scheduled to merge with another queue, be
         * sure to drop the reference taken on that queue (and others in
         * the merge chain).  See cfq_setup_merge and cfq_merge_cfqqs.
         */
        __cfqq = cfqq->new_cfqq;
        while (__cfqq) {
                if (__cfqq == cfqq) {
                        WARN(1, "cfqq->new_cfqq loop detected\n");
                        break;
                }
                next = __cfqq->new_cfqq;
                cfq_put_queue(__cfqq);
                __cfqq = next;
        }
}

static void cfq_exit_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
        if (unlikely(cfqq == cfqd->active_queue)) {
                __cfq_slice_expired(cfqd, cfqq, 0);
                cfq_schedule_dispatch(cfqd);
        }

        cfq_put_cooperator(cfqq);

        cfq_put_queue(cfqq);
}

static void __cfq_exit_single_io_context(struct cfq_data *cfqd,
                                         struct cfq_io_context *cic)
{
        struct io_context *ioc = cic->ioc;

        list_del_init(&cic->queue_list);

        /*
         * Make sure dead mark is seen for dead queues
         */
        smp_wmb();
        cic->key = cfqd_dead_key(cfqd);

        if (ioc->ioc_data == cic)
                rcu_assign_pointer(ioc->ioc_data, NULL);

        if (cic->cfqq[BLK_RW_ASYNC]) {
                cfq_exit_cfqq(cfqd, cic->cfqq[BLK_RW_ASYNC]);
                cic->cfqq[BLK_RW_ASYNC] = NULL;
        }

        if (cic->cfqq[BLK_RW_SYNC]) {
                cfq_exit_cfqq(cfqd, cic->cfqq[BLK_RW_SYNC]);
                cic->cfqq[BLK_RW_SYNC] = NULL;
        }
}

static void cfq_exit_single_io_context(struct io_context *ioc,
                                       struct cfq_io_context *cic)
{
        struct cfq_data *cfqd = cic_to_cfqd(cic);

        if (cfqd) {
                struct request_queue *q = cfqd->queue;
                unsigned long flags;

                spin_lock_irqsave(q->queue_lock, flags);

                /*
                 * Ensure we get a fresh copy of the ->key to prevent
                 * race between exiting task and queue
                 */
                smp_read_barrier_depends();
                if (cic->key == cfqd)
                        __cfq_exit_single_io_context(cfqd, cic);

                spin_unlock_irqrestore(q->queue_lock, flags);
        }
}

/*
 * The process that ioc belongs to has exited, we need to clean up
 * and put the internal structures we have that belongs to that process.
 */
static void cfq_exit_io_context(struct io_context *ioc)
{
        call_for_each_cic(ioc, cfq_exit_single_io_context);
}

static struct cfq_io_context *
cfq_alloc_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
{
        struct cfq_io_context *cic;

        cic = kmem_cache_alloc_node(cfq_ioc_pool, gfp_mask | __GFP_ZERO,
                                                        cfqd->queue->node);
        if (cic) {
                cic->last_end_request = jiffies;
                INIT_LIST_HEAD(&cic->queue_list);
                INIT_HLIST_NODE(&cic->cic_list);
                cic->dtor = cfq_free_io_context;
                cic->exit = cfq_exit_io_context;
                elv_ioc_count_inc(cfq_ioc_count);
        }

        return cic;
}

static void cfq_init_prio_data(struct cfq_queue *cfqq, struct io_context *ioc)
{
        struct task_struct *tsk = current;
        int ioprio_class;

        if (!cfq_cfqq_prio_changed(cfqq))
                return;

        ioprio_class = IOPRIO_PRIO_CLASS(ioc->ioprio);
        switch (ioprio_class) {
        default:
                printk(KERN_ERR "cfq: bad prio %x\n", ioprio_class);
        case IOPRIO_CLASS_NONE:
                /*
                 * no prio set, inherit CPU scheduling settings
                 */
                cfqq->ioprio = task_nice_ioprio(tsk);
                cfqq->ioprio_class = task_nice_ioclass(tsk);
                break;
        case IOPRIO_CLASS_RT:
                cfqq->ioprio = task_ioprio(ioc);
                cfqq->ioprio_class = IOPRIO_CLASS_RT;
                break;
        case IOPRIO_CLASS_BE:
                cfqq->ioprio = task_ioprio(ioc);
                cfqq->ioprio_class = IOPRIO_CLASS_BE;
                break;
        case IOPRIO_CLASS_IDLE:
                cfqq->ioprio_class = IOPRIO_CLASS_IDLE;
                cfqq->ioprio = 7;
                cfq_clear_cfqq_idle_window(cfqq);
                break;
        }

        /*
         * keep track of original prio settings in case we have to temporarily
         * elevate the priority of this queue
         */
        cfqq->org_ioprio = cfqq->ioprio;
        cfqq->org_ioprio_class = cfqq->ioprio_class;
        cfq_clear_cfqq_prio_changed(cfqq);
}

static void changed_ioprio(struct io_context *ioc, struct cfq_io_context *cic)
{
        struct cfq_data *cfqd = cic_to_cfqd(cic);
        struct cfq_queue *cfqq;
        unsigned long flags;

        if (unlikely(!cfqd))
                return;

        spin_lock_irqsave(cfqd->queue->queue_lock, flags);

        cfqq = cic->cfqq[BLK_RW_ASYNC];
        if (cfqq) {
                struct cfq_queue *new_cfqq;
                new_cfqq = cfq_get_queue(cfqd, BLK_RW_ASYNC, cic->ioc,
                                                GFP_ATOMIC);
                if (new_cfqq) {
                        cic->cfqq[BLK_RW_ASYNC] = new_cfqq;
                        cfq_put_queue(cfqq);
                }
        }

        cfqq = cic->cfqq[BLK_RW_SYNC];
        if (cfqq)
                cfq_mark_cfqq_prio_changed(cfqq);

        spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
}

static void cfq_ioc_set_ioprio(struct io_context *ioc)
{
        call_for_each_cic(ioc, changed_ioprio);
        ioc->ioprio_changed = 0;
}

static void cfq_init_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                          pid_t pid, bool is_sync)
{
        RB_CLEAR_NODE(&cfqq->rb_node);
        RB_CLEAR_NODE(&cfqq->p_node);
        INIT_LIST_HEAD(&cfqq->fifo);

        cfqq->ref = 0;
        cfqq->cfqd = cfqd;

        cfq_mark_cfqq_prio_changed(cfqq);

        if (is_sync) {
                if (!cfq_class_idle(cfqq))
                        cfq_mark_cfqq_idle_window(cfqq);
                cfq_mark_cfqq_sync(cfqq);
        }
        cfqq->pid = pid;
}

#ifdef CONFIG_CFQ_GROUP_IOSCHED
static void changed_cgroup(struct io_context *ioc, struct cfq_io_context *cic)
{
        struct cfq_queue *sync_cfqq = cic_to_cfqq(cic, 1);
        struct cfq_data *cfqd = cic_to_cfqd(cic);
        unsigned long flags;
        struct request_queue *q;

        if (unlikely(!cfqd))
                return;

        q = cfqd->queue;

        spin_lock_irqsave(q->queue_lock, flags);

        if (sync_cfqq) {
                /*
                 * Drop reference to sync queue. A new sync queue will be
                 * assigned in new group upon arrival of a fresh request.
                 */
                cfq_log_cfqq(cfqd, sync_cfqq, "changed cgroup");
                cic_set_cfqq(cic, NULL, 1);
                cfq_put_queue(sync_cfqq);
        }

        spin_unlock_irqrestore(q->queue_lock, flags);
}

static void cfq_ioc_set_cgroup(struct io_context *ioc)
{
        call_for_each_cic(ioc, changed_cgroup);
        ioc->cgroup_changed = 0;
}
#endif  /* CONFIG_CFQ_GROUP_IOSCHED */

static struct cfq_queue *
cfq_find_alloc_queue(struct cfq_data *cfqd, bool is_sync,
                     struct io_context *ioc, gfp_t gfp_mask)
{
        struct cfq_queue *cfqq, *new_cfqq = NULL;
        struct cfq_io_context *cic;
        struct cfq_group *cfqg;

retry:
        cfqg = cfq_get_cfqg(cfqd, 1);
        cic = cfq_cic_lookup(cfqd, ioc);
        /* cic always exists here */
        cfqq = cic_to_cfqq(cic, is_sync);

        /*
         * Always try a new alloc if we fell back to the OOM cfqq
         * originally, since it should just be a temporary situation.
         */
        if (!cfqq || cfqq == &cfqd->oom_cfqq) {
                cfqq = NULL;
                if (new_cfqq) {
                        cfqq = new_cfqq;
                        new_cfqq = NULL;
                } else if (gfp_mask & __GFP_WAIT) {
                        spin_unlock_irq(cfqd->queue->queue_lock);
                        new_cfqq = kmem_cache_alloc_node(cfq_pool,
                                        gfp_mask | __GFP_ZERO,
                                        cfqd->queue->node);
                        spin_lock_irq(cfqd->queue->queue_lock);
                        if (new_cfqq)
                                goto retry;
                } else {
                        cfqq = kmem_cache_alloc_node(cfq_pool,
                                        gfp_mask | __GFP_ZERO,
                                        cfqd->queue->node);
                }

                if (cfqq) {
                        cfq_init_cfqq(cfqd, cfqq, current->pid, is_sync);
                        cfq_init_prio_data(cfqq, ioc);
                        cfq_link_cfqq_cfqg(cfqq, cfqg);
                        cfq_log_cfqq(cfqd, cfqq, "alloced");
                } else
                        cfqq = &cfqd->oom_cfqq;
        }

        if (new_cfqq)
                kmem_cache_free(cfq_pool, new_cfqq);

        return cfqq;
}

static struct cfq_queue **
cfq_async_queue_prio(struct cfq_data *cfqd, int ioprio_class, int ioprio)
{
        switch (ioprio_class) {
        case IOPRIO_CLASS_RT:
                return &cfqd->async_cfqq[0][ioprio];
        case IOPRIO_CLASS_BE:
                return &cfqd->async_cfqq[1][ioprio];
        case IOPRIO_CLASS_IDLE:
                return &cfqd->async_idle_cfqq;
        default:
                BUG();
        }
}

static struct cfq_queue *
cfq_get_queue(struct cfq_data *cfqd, bool is_sync, struct io_context *ioc,
              gfp_t gfp_mask)
{
        const int ioprio = task_ioprio(ioc);
        const int ioprio_class = task_ioprio_class(ioc);
        struct cfq_queue **async_cfqq = NULL;
        struct cfq_queue *cfqq = NULL;

        if (!is_sync) {
                async_cfqq = cfq_async_queue_prio(cfqd, ioprio_class, ioprio);
                cfqq = *async_cfqq;
        }

        if (!cfqq)
                cfqq = cfq_find_alloc_queue(cfqd, is_sync, ioc, gfp_mask);

        /*
         * pin the queue now that it's allocated, scheduler exit will prune it
         */
        if (!is_sync && !(*async_cfqq)) {
                cfqq->ref++;
                *async_cfqq = cfqq;
        }

        cfqq->ref++;
        return cfqq;
}

/*
 * We drop cfq io contexts lazily, so we may find a dead one.
 */
static void