LXR linux/block/blk-softirq.c

   1/*
   2 * Functions related to softirq rq completions
   3 */
   4#include <linux/kernel.h>
   5#include <linux/module.h>
   6#include <linux/init.h>
   7#include <linux/bio.h>
   8#include <linux/blkdev.h>
   9#include <linux/interrupt.h>
  10#include <linux/cpu.h>
  11#include <linux/sched.h>
  12
  13#include "blk.h"
  14
  15static DEFINE_PER_CPU(struct list_head, blk_cpu_done);
  16
  17/*
  18 * Softirq action handler - move entries to local list and loop over them
  19 * while passing them to the queue registered handler.
  20 */
  21static __latent_entropy void blk_done_softirq(struct softirq_action *h)
  22{
  23        struct list_head *cpu_list, local_list;
  24
  25        local_irq_disable();
  26        cpu_list = this_cpu_ptr(&blk_cpu_done);
  27        list_replace_init(cpu_list, &local_list);
  28        local_irq_enable();
  29
  30        while (!list_empty(&local_list)) {
  31                struct request *rq;
  32
  33                rq = list_entry(local_list.next, struct request, ipi_list);
  34                list_del_init(&rq->ipi_list);
  35                rq->q->softirq_done_fn(rq);
  36        }
  37}
  38
  39#ifdef CONFIG_SMP
  40static void trigger_softirq(void *data)
  41{
  42        struct request *rq = data;
  43        unsigned long flags;
  44        struct list_head *list;
  45
  46        local_irq_save(flags);
  47        list = this_cpu_ptr(&blk_cpu_done);
  48        list_add_tail(&rq->ipi_list, list);
  49
  50        if (list->next == &rq->ipi_list)
  51                raise_softirq_irqoff(BLOCK_SOFTIRQ);
  52
  53        local_irq_restore(flags);
  54}
  55
  56/*
  57 * Setup and invoke a run of 'trigger_softirq' on the given cpu.
  58 */
  59static int raise_blk_irq(int cpu, struct request *rq)
  60{
  61        if (cpu_online(cpu)) {
  62                struct call_single_data *data = &rq->csd;
  63
  64                data->func = trigger_softirq;
  65                data->info = rq;
  66                data->flags = 0;
  67
  68                smp_call_function_single_async(cpu, data);
  69                return 0;
  70        }
  71
  72        return 1;
  73}
  74#else /* CONFIG_SMP */
  75static int raise_blk_irq(int cpu, struct request *rq)
  76{
  77        return 1;
  78}
  79#endif
  80
  81static int blk_softirq_cpu_dead(unsigned int cpu)
  82{
  83        /*
  84         * If a CPU goes away, splice its entries to the current CPU
  85         * and trigger a run of the softirq
  86         */
  87        local_irq_disable();
  88        list_splice_init(&per_cpu(blk_cpu_done, cpu),
  89                         this_cpu_ptr(&blk_cpu_done));
  90        raise_softirq_irqoff(BLOCK_SOFTIRQ);
  91        local_irq_enable();
  92
  93        return 0;
  94}
  95
  96void __blk_complete_request(struct request *req)
  97{
  98        int ccpu, cpu;
  99        struct request_queue *q = req->q;
 100        unsigned long flags;
 101        bool shared = false;
 102
 103        BUG_ON(!q->softirq_done_fn);
 104
 105        local_irq_save(flags);
 106        cpu = smp_processor_id();
 107
 108        /*
 109         * Select completion CPU
 110         */
 111        if (req->cpu != -1) {
 112                ccpu = req->cpu;
 113                if (!test_bit(QUEUE_FLAG_SAME_FORCE, &q->queue_flags))
 114                        shared = cpus_share_cache(cpu, ccpu);
 115        } else
 116                ccpu = cpu;
 117
 118        /*
 119         * If current CPU and requested CPU share a cache, run the softirq on
 120         * the current CPU. One might concern this is just like
 121         * QUEUE_FLAG_SAME_FORCE, but actually not. blk_complete_request() is
 122         * running in interrupt handler, and currently I/O controller doesn't
 123         * support multiple interrupts, so current CPU is unique actually. This
 124         * avoids IPI sending from current CPU to the first CPU of a group.
 125         */
 126        if (ccpu == cpu || shared) {
 127                struct list_head *list;
 128do_local:
 129                list = this_cpu_ptr(&blk_cpu_done);
 130                list_add_tail(&req->ipi_list, list);
 131
 132                /*
 133                 * if the list only contains our just added request,
 134                 * signal a raise of the softirq. If there are already
 135                 * entries there, someone already raised the irq but it
 136                 * hasn't run yet.
 137                 */
 138                if (list->next == &req->ipi_list)
 139                        raise_softirq_irqoff(BLOCK_SOFTIRQ);
 140        } else if (raise_blk_irq(ccpu, req))
 141                goto do_local;
 142
 143        local_irq_restore(flags);
 144}
 145
 146/**
 147 * blk_complete_request - end I/O on a request
 148 * @req:      the request being processed
 149 *
 150 * Description:
 151 *     Ends all I/O on a request. It does not handle partial completions,
 152 *     unless the driver actually implements this in its completion callback
 153 *     through requeueing. The actual completion happens out-of-order,
 154 *     through a softirq handler. The user must have registered a completion
 155 *     callback through blk_queue_softirq_done().
 156 **/
 157void blk_complete_request(struct request *req)
 158{
 159        if (unlikely(blk_should_fake_timeout(req->q)))
 160                return;
 161        if (!blk_mark_rq_complete(req))
 162                __blk_complete_request(req);
 163}
 164EXPORT_SYMBOL(blk_complete_request);
 165
 166static __init int blk_softirq_init(void)
 167{
 168        int i;
 169
 170        for_each_possible_cpu(i)
 171                INIT_LIST_HEAD(&per_cpu(blk_cpu_done, i));
 172
 173        open_softirq(BLOCK_SOFTIRQ, blk_done_softirq);
 174        cpuhp_setup_state_nocalls(CPUHP_BLOCK_SOFTIRQ_DEAD,
 175                                  "block/softirq:dead", NULL,
 176                                  blk_softirq_cpu_dead);
 177        return 0;
 178}
 179subsys_initcall(blk_softirq_init);
 180