/*
 *  MQ Deadline i/o scheduler - adaptation of the legacy deadline scheduler,
 *  for the blk-mq scheduling framework
 *
 *  Copyright (C) 2016 Jens Axboe <axboe@kernel.dk>
 */
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/blkdev.h>
#include <linux/blk-mq.h>
#include <linux/elevator.h>
#include <linux/bio.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/compiler.h>
#include <linux/rbtree.h>
#include <linux/sbitmap.h>

#include "blk.h"
#include "blk-mq.h"
#include "blk-mq-debugfs.h"
#include "blk-mq-tag.h"
#include "blk-mq-sched.h"

/*
 * See Documentation/block/deadline-iosched.txt
 */
static const int read_expire = HZ / 2;  /* max time before a read is submitted. */
static const int write_expire = 5 * HZ; /* ditto for writes, these limits are SOFT! */
static const int writes_starved = 2;    /* max times reads can starve a write */
static const int fifo_batch = 16;       /* # of sequential requests treated as one
                                     by the above parameters. For throughput. */

struct deadline_data {
        /*
         * run time data
         */

        /*
         * requests (deadline_rq s) are present on both sort_list and fifo_list
         */
        struct rb_root sort_list[2];
        struct list_head fifo_list[2];

        /*
         * next in sort order. read, write or both are NULL
         */
        struct request *next_rq[2];
        unsigned int batching;          /* number of sequential requests made */
        unsigned int starved;           /* times reads have starved writes */

        /*
         * settings that change how the i/o scheduler behaves
         */
        int fifo_expire[2];
        int fifo_batch;
        int writes_starved;
        int front_merges;

        spinlock_t lock;
        struct list_head dispatch;
};

static inline struct rb_root *
deadline_rb_root(struct deadline_data *dd, struct request *rq)
{
        return &dd->sort_list[rq_data_dir(rq)];
}

/*
 * get the request after `rq' in sector-sorted order
 */
static inline struct request *
deadline_latter_request(struct request *rq)
{
        struct rb_node *node = rb_next(&rq->rb_node);

        if (node)
                return rb_entry_rq(node);

        return NULL;
}

static void
deadline_add_rq_rb(struct deadline_data *dd, struct request *rq)
{
        struct rb_root *root = deadline_rb_root(dd, rq);

        elv_rb_add(root, rq);
}

static inline void
deadline_del_rq_rb(struct deadline_data *dd, struct request *rq)
{
        const int data_dir = rq_data_dir(rq);

        if (dd->next_rq[data_dir] == rq)
                dd->next_rq[data_dir] = deadline_latter_request(rq);

        elv_rb_del(deadline_rb_root(dd, rq), rq);
}

/*
 * remove rq from rbtree and fifo.
 */
static void deadline_remove_request(struct request_queue *q, struct request *rq)
{
        struct deadline_data *dd = q->elevator->elevator_data;

        list_del_init(&rq->queuelist);

        /*
         * We might not be on the rbtree, if we are doing an insert merge
         */
        if (!RB_EMPTY_NODE(&rq->rb_node))
                deadline_del_rq_rb(dd, rq);

        elv_rqhash_del(q, rq);
        if (q->last_merge == rq)
                q->last_merge = NULL;
}

static void dd_request_merged(struct request_queue *q, struct request *req,
                              enum elv_merge type)
{
        struct deadline_data *dd = q->elevator->elevator_data;

        /*
         * if the merge was a front merge, we need to reposition request
         */
        if (type == ELEVATOR_FRONT_MERGE) {
                elv_rb_del(deadline_rb_root(dd, req), req);
                deadline_add_rq_rb(dd, req);
        }
}

static void dd_merged_requests(struct request_queue *q, struct request *req,
                               struct request *next)
{
        /*
         * if next expires before rq, assign its expire time to rq
         * and move into next position (next will be deleted) in fifo
         */
        if (!list_empty(&req->queuelist) && !list_empty(&next->queuelist)) {
                if (time_before((unsigned long)next->fifo_time,
                                (unsigned long)req->fifo_time)) {
                        list_move(&req->queuelist, &next->queuelist);
                        req->fifo_time = next->fifo_time;
                }
        }

        /*
         * kill knowledge of next, this one is a goner
         */
        deadline_remove_request(q, next);
}

/*
 * move an entry to dispatch queue
 */
static void
deadline_move_request(struct deadline_data *dd, struct request *rq)
{
        const int data_dir = rq_data_dir(rq);

        dd->next_rq[READ] = NULL;
        dd->next_rq[WRITE] = NULL;
        dd->next_rq[data_dir] = deadline_latter_request(rq);

        /*
         * take it off the sort and fifo list
         */
        deadline_remove_request(rq->q, rq);
}

/*
 * deadline_check_fifo returns 0 if there are no expired requests on the fifo,
 * 1 otherwise. Requires !list_empty(&dd->fifo_list[data_dir])
 */
static inline int deadline_check_fifo(struct deadline_data *dd, int ddir)
{
        struct request *rq = rq_entry_fifo(dd->fifo_list[ddir].next);

        /*
         * rq is expired!
         */
        if (time_after_eq(jiffies, (unsigned long)rq->fifo_time))
                return 1;

        return 0;
}

/*
 * deadline_dispatch_requests selects the best request according to
 * read/write expire, fifo_batch, etc
 */
static struct request *__dd_dispatch_request(struct blk_mq_hw_ctx *hctx)
{
        struct deadline_data *dd = hctx->queue->elevator->elevator_data;
        struct request *rq;
        bool reads, writes;
        int data_dir;

        if (!list_empty(&dd->dispatch)) {
                rq = list_first_entry(&dd->dispatch, struct request, queuelist);
                list_del_init(&rq->queuelist);
                goto done;
        }

        reads = !list_empty(&dd->fifo_list[READ]);
        writes = !list_empty(&dd->fifo_list[WRITE]);

        /*
         * batches are currently reads XOR writes
         */
        if (dd->next_rq[WRITE])
                rq = dd->next_rq[WRITE];
        else
                rq = dd->next_rq[READ];

        if (rq && dd->batching < dd->fifo_batch)
                /* we have a next request are still entitled to batch */
                goto dispatch_request;

        /*
         * at this point we are not running a batch. select the appropriate
         * data direction (read / write)
         */

        if (reads) {
                BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[READ]));

                if (writes && (dd->starved++ >= dd->writes_starved))
                        goto dispatch_writes;

                data_dir = READ;

                goto dispatch_find_request;
        }

        /*
         * there are either no reads or writes have been starved
         */

        if (writes) {
dispatch_writes:
                BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[WRITE]));

                dd->starved = 0;

                data_dir = WRITE;

                goto dispatch_find_request;
        }

        return NULL;

dispatch_find_request:
        /*
         * we are not running a batch, find best request for selected data_dir
         */
        if (deadline_check_fifo(dd, data_dir) || !dd->next_rq[data_dir]) {
                /*
                 * A deadline has expired, the last request was in the other
                 * direction, or we have run out of higher-sectored requests.
                 * Start again from the request with the earliest expiry time.
                 */
                rq = rq_entry_fifo(dd->fifo_list[data_dir].next);
        } else {
                /*
                 * The last req was the same dir and we have a next request in
                 * sort order. No expired requests so continue on from here.
                 */
                rq = dd->next_rq[data_dir];
        }

        dd->batching = 0;

dispatch_request:
        /*
         * rq is the selected appropriate request.
         */
        dd->batching++;
        deadline_move_request(dd, rq);
done:
        rq->rq_flags |= RQF_STARTED;
        return rq;
}

static struct request *dd_dispatch_request(struct blk_mq_hw_ctx *hctx)
{
        struct deadline_data *dd = hctx->queue->elevator->elevator_data;
        struct request *rq;

        spin_lock(&dd->lock);
        rq = __dd_dispatch_request(hctx);
        spin_unlock(&dd->lock);

        return rq;
}

static void dd_exit_queue(struct elevator_queue *e)
{
        struct deadline_data *dd = e->elevator_data;

        BUG_ON(!list_empty(&dd->fifo_list[READ]));
        BUG_ON(!list_empty(&dd->fifo_list[WRITE]));

        kfree(dd);
}

/*
 * initialize elevator private data (deadline_data).
 */
static int dd_init_queue(struct request_queue *q, struct elevator_type *e)
{
        struct deadline_data *dd;
        struct elevator_queue *eq;

        eq = elevator_alloc(q, e);
        if (!eq)
                return -ENOMEM;

        dd = kzalloc_node(sizeof(*dd), GFP_KERNEL, q->node);
        if (!dd) {
                kobject_put(&eq->kobj);
                return -ENOMEM;
        }
        eq->elevator_data = dd;

        INIT_LIST_HEAD(&dd->fifo_list[READ]);
        INIT_LIST_HEAD(&dd->fifo_list[WRITE]);
        dd->sort_list[READ] = RB_ROOT;
        dd->sort_list[WRITE] = RB_ROOT;
        dd->fifo_expire[READ] = read_expire;
        dd->fifo_expire[WRITE] = write_expire;
        dd->writes_starved = writes_starved;
        dd->front_merges = 1;
        dd->fifo_batch = fifo_batch;
        spin_lock_init(&dd->lock);
        INIT_LIST_HEAD(&dd->dispatch);

        q->elevator = eq;
        return 0;
}

static int dd_request_merge(struct request_queue *q, struct request **rq,
                            struct bio *bio)
{
        struct deadline_data *dd = q->elevator->elevator_data;
        sector_t sector = bio_end_sector(bio);
        struct request *__rq;

        if (!dd->front_merges)
                return ELEVATOR_NO_MERGE;

        __rq = elv_rb_find(&dd->sort_list[bio_data_dir(bio)], sector);
        if (__rq) {
                BUG_ON(sector != blk_rq_pos(__rq));

                if (elv_bio_merge_ok(__rq, bio)) {
                        *rq = __rq;
                        return ELEVATOR_FRONT_MERGE;
                }
        }

        return ELEVATOR_NO_MERGE;
}

static bool dd_bio_merge(struct blk_mq_hw_ctx *hctx, struct bio *bio)
{
        struct request_queue *q = hctx->queue;
        struct deadline_data *dd = q->elevator->elevator_data;
        struct request *free = NULL;
        bool ret;

        spin_lock(&dd->lock);
        ret = blk_mq_sched_try_merge(q, bio, &free);
        spin_unlock(&dd->lock);

        if (free)
                blk_mq_free_request(free);

        return ret;
}

/*
 * add rq to rbtree and fifo
 */
static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
                              bool at_head)
{
        struct request_queue *q = hctx->queue;
        struct deadline_data *dd = q->elevator->elevator_data;
        const int data_dir = rq_data_dir(rq);

        if (blk_mq_sched_try_insert_merge(q, rq))
                return;

        blk_mq_sched_request_inserted(rq);

        if (at_head || blk_rq_is_passthrough(rq)) {
                if (at_head)
                        list_add(&rq->queuelist, &dd->dispatch);
                else
                        list_add_tail(&rq->queuelist, &dd->dispatch);
        } else {
                deadline_add_rq_rb(dd, rq);

                if (rq_mergeable(rq)) {
                        elv_rqhash_add(q, rq);
                        if (!q->last_merge)
                                q->last_merge = rq;
                }

                /*
                 * set expire time and add to fifo list
                 */
                rq->fifo_time = jiffies + dd->fifo_expire[data_dir];
                list_add_tail(&rq->queuelist, &dd->fifo_list[data_dir]);
        }
}

static void dd_insert_requests(struct blk_mq_hw_ctx *hctx,
                               struct list_head *list, bool at_head)
{
        struct request_queue *q = hctx->queue;
        struct deadline_data *dd = q->elevator->elevator_data;

        spin_lock(&dd->lock);
        while (!list_empty(list)) {
                struct request *rq;

                rq = list_first_entry(list, struct request, queuelist);
                list_del_init(&rq->queuelist);
                dd_insert_request(hctx, rq, at_head);
        }
        spin_unlock(&dd->lock);
}

static bool dd_has_work(struct blk_mq_hw_ctx *hctx)
{
        struct deadline_data *dd = hctx->queue->elevator->elevator_data;

        return !list_empty_careful(&dd->dispatch) ||
                !list_empty_careful(&dd->fifo_list[0]) ||
                !list_empty_careful(&dd->fifo_list[1]);
}

/*
 * sysfs parts below
 */
static ssize_t
deadline_var_show(int var, char *page)
{
        return sprintf(page, "%d\n", var);
}

static ssize_t
deadline_var_store(int *var, const char *page, size_t count)
{
        char *p = (char *) page;

        *var = simple_strtol(p, &p, 10);
        return count;
}

#define SHOW_FUNCTION(__FUNC, __VAR, __CONV)                            \
static ssize_t __FUNC(struct elevator_queue *e, char *page)             \
{                                                                       \
        struct deadline_data *dd = e->elevator_data;                    \
        int __data = __VAR;                                             \
        if (__CONV)                                                     \
                __data = jiffies_to_msecs(__data);                      \
        return deadline_var_show(__data, (page));                       \
}
SHOW_FUNCTION(deadline_read_expire_show, dd->fifo_expire[READ], 1);
SHOW_FUNCTION(deadline_write_expire_show, dd->fifo_expire[WRITE], 1);
SHOW_FUNCTION(deadline_writes_starved_show, dd->writes_starved, 0);
SHOW_FUNCTION(deadline_front_merges_show, dd->front_merges, 0);
SHOW_FUNCTION(deadline_fifo_batch_show, dd->fifo_batch, 0);
#undef SHOW_FUNCTION

#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV)                 \
static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count) \
{                                                                       \
        struct deadline_data *dd = e->elevator_data;                    \
        int __data;                                                     \
        int ret = deadline_var_store(&__data, (page), count);           \
        if (__data < (MIN))                                             \
                __data = (MIN);                                         \
        else if (__data > (MAX))                                        \
                __data = (MAX);                                         \
        if (__CONV)                                                     \
                *(__PTR) = msecs_to_jiffies(__data);                    \
        else                                                            \
                *(__PTR) = __data;                                      \
        return ret;                                                     \
}
STORE_FUNCTION(deadline_read_expire_store, &dd->fifo_expire[READ], 0, INT_MAX, 1);
STORE_FUNCTION(deadline_write_expire_store, &dd->fifo_expire[WRITE], 0, INT_MAX, 1);
STORE_FUNCTION(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX, 0);
STORE_FUNCTION(deadline_front_merges_store, &dd->front_merges, 0, 1, 0);
STORE_FUNCTION(deadline_fifo_batch_store, &dd->fifo_batch, 0, INT_MAX, 0);
#undef STORE_FUNCTION

#define DD_ATTR(name) \
        __ATTR(name, S_IRUGO|S_IWUSR, deadline_##name##_show, \
                                      deadline_##name##_store)

static struct elv_fs_entry deadline_attrs[] = {
        DD_ATTR(read_expire),
        DD_ATTR(write_expire),
        DD_ATTR(writes_starved),
        DD_ATTR(front_merges),
        DD_ATTR(fifo_batch),
        __ATTR_NULL
};

#ifdef CONFIG_BLK_DEBUG_FS
#define DEADLINE_DEBUGFS_DDIR_ATTRS(ddir, name)                         \
static void *deadline_##name##_fifo_start(struct seq_file *m,           \
                                          loff_t *pos)                  \
        __acquires(&dd->lock)                                           \
{                                                                       \
        struct request_queue *q = m->private;                           \
        struct deadline_data *dd = q->elevator->elevator_data;          \
                                                                        \
        spin_lock(&dd->lock);                                           \
        return seq_list_start(&dd->fifo_list[ddir], *pos);              \
}                                                                       \
                                                                        \
static void *deadline_##name##_fifo_next(struct seq_file *m, void *v,   \
                                         loff_t *pos)                   \
{                                                                       \
        struct request_queue *q = m->private;                           \
        struct deadline_data *dd = q->elevator->elevator_data;          \
                                                                        \
        return seq_list_next(v, &dd->fifo_list[ddir], pos);             \
}                                                                       \
                                                                        \
static void deadline_##name##_fifo_stop(struct seq_file *m, void *v)    \
        __releases(&dd->lock)                                           \
{                                                                       \
        struct request_queue *q = m->private;                           \
        struct deadline_data *dd = q->elevator->elevator_data;          \
                                                                        \
        spin_unlock(&dd->lock);                                         \
}                                                                       \
                                                                        \
static const struct seq_operations deadline_##name##_fifo_seq_ops = {   \
        .start  = deadline_##name##_fifo_start,                         \
        .next   = deadline_##name##_fifo_next,                          \
        .stop   = deadline_##name##_fifo_stop,                          \
        .show   = blk_mq_debugfs_rq_show,                               \
};                                                                      \
                                                                        \
static int deadline_##name##_next_rq_show(void *data,                   \
                                          struct seq_file *m)           \
{                                                                       \
        struct request_queue *q = data;                                 \
        struct deadline_data *dd = q->elevator->elevator_data;          \
        struct request *rq = dd->next_rq[ddir];                         \
                                                                        \
        if (rq)                                                         \
                __blk_mq_debugfs_rq_show(m, rq);                        \
        return 0;                                                       \
}
DEADLINE_DEBUGFS_DDIR_ATTRS(READ, read)
DEADLINE_DEBUGFS_DDIR_ATTRS(WRITE, write)
#undef DEADLINE_DEBUGFS_DDIR_ATTRS

static int deadline_batching_show(void *data, struct seq_file *m)
{
        struct request_queue *q = data;
        struct deadline_data *dd = q->elevator->elevator_data;

        seq_printf(m, "%u\n", dd->batching);
        return 0;
}

static int deadline_starved_show(void *data, struct seq_file *m)
{
        struct request_queue *q = data;
        struct deadline_data *dd = q->elevator->elevator_data;

        seq_printf(m, "%u\n", dd->starved);
        return 0;
}

static void *deadline_dispatch_start(struct seq_file *m, loff_t *pos)
        __acquires(&dd->lock)
{
        struct request_queue *q = m->private;
        struct deadline_data *dd = q->elevator->elevator_data;

        spin_lock(&dd->lock);
        return seq_list_start(&dd->dispatch, *pos);
}

static void *deadline_dispatch_next(struct seq_file *m, void *v, loff_t *pos)
{
        struct request_queue *q = m->private;
        struct deadline_data *dd = q->elevator->elevator_data;

        return seq_list_next(v, &dd->dispatch, pos);
}

static void deadline_dispatch_stop(struct seq_file *m, void *v)
        __releases(&dd->lock)
{
        struct request_queue *q = m->private;
        struct deadline_data *dd = q->elevator->elevator_data;

        spin_unlock(&dd->lock);
}

static const struct seq_operations deadline_dispatch_seq_ops = {
        .start  = deadline_dispatch_start,
        .next   = deadline_dispatch_next,
        .stop   = deadline_dispatch_stop,
        .show   = blk_mq_debugfs_rq_show,
};

#define DEADLINE_QUEUE_DDIR_ATTRS(name)                                         \
        {#name "_fifo_list", 0400, .seq_ops = &deadline_##name##_fifo_seq_ops}, \
        {#name "_next_rq", 0400, deadline_##name##_next_rq_show}
static const struct blk_mq_debugfs_attr deadline_queue_debugfs_attrs[] = {
        DEADLINE_QUEUE_DDIR_ATTRS(read),
        DEADLINE_QUEUE_DDIR_ATTRS(write),
        {"batching", 0400, deadline_batching_show},
        {"starved", 0400, deadline_starved_show},
        {"dispatch", 0400, .seq_ops = &deadline_dispatch_seq_ops},
        {},
};
#undef DEADLINE_QUEUE_DDIR_ATTRS
#endif

static struct elevator_type mq_deadline = {
        .ops.mq = {
                .insert_requests        = dd_insert_requests,
                .dispatch_request       = dd_dispatch_request,
                .next_request           = elv_rb_latter_request,
                .former_request         = elv_rb_former_request,
                .bio_merge              = dd_bio_merge,
                .request_merge          = dd_request_merge,
                .requests_merged        = dd_merged_requests,
                .request_merged         = dd_request_merged,
                .has_work               = dd_has_work,
                .init_sched             = dd_init_queue,
                .exit_sched             = dd_exit_queue,
        },

        .uses_mq        = true,
#ifdef CONFIG_BLK_DEBUG_FS
        .queue_debugfs_attrs = deadline_queue_debugfs_attrs,
#endif
        .elevator_attrs = deadline_attrs,
        .elevator_name = "mq-deadline",
        .elevator_owner = THIS_MODULE,
};

static int __init deadline_init(void)
{
        return elv_register(&mq_deadline);
}

static void __exit deadline_exit(void)
{
        elv_unregister(&mq_deadline);
}

module_init(deadline_init);
module_exit(deadline_exit);

MODULE_AUTHOR("Jens Axboe");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("MQ deadline IO scheduler");