linux/block/blk-softirq.c
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   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 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 = &__get_cpu_var(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, csd.list);
  34                list_del_init(&rq->csd.list);
  35                rq->q->softirq_done_fn(rq);
  36        }
  37}
  38
  39#if defined(CONFIG_SMP) && defined(CONFIG_USE_GENERIC_SMP_HELPERS)
  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 = &__get_cpu_var(blk_cpu_done);
  48        list_add_tail(&rq->csd.list, list);
  49
  50        if (list->next == &rq->csd.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(cpu, data, 0);
  69                return 0;
  70        }
  71
  72        return 1;
  73}
  74#else /* CONFIG_SMP && CONFIG_USE_GENERIC_SMP_HELPERS */
  75static int raise_blk_irq(int cpu, struct request *rq)
  76{
  77        return 1;
  78}
  79#endif
  80
  81static int __cpuinit blk_cpu_notify(struct notifier_block *self,
  82                                    unsigned long action, void *hcpu)
  83{
  84        /*
  85         * If a CPU goes away, splice its entries to the current CPU
  86         * and trigger a run of the softirq
  87         */
  88        if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
  89                int cpu = (unsigned long) hcpu;
  90
  91                local_irq_disable();
  92                list_splice_init(&per_cpu(blk_cpu_done, cpu),
  93                                 &__get_cpu_var(blk_cpu_done));
  94                raise_softirq_irqoff(BLOCK_SOFTIRQ);
  95                local_irq_enable();
  96        }
  97
  98        return NOTIFY_OK;
  99}
 100
 101static struct notifier_block __cpuinitdata blk_cpu_notifier = {
 102        .notifier_call  = blk_cpu_notify,
 103};
 104
 105void __blk_complete_request(struct request *req)
 106{
 107        int ccpu, cpu;
 108        struct request_queue *q = req->q;
 109        unsigned long flags;
 110        bool shared = false;
 111
 112        BUG_ON(!q->softirq_done_fn);
 113
 114        local_irq_save(flags);
 115        cpu = smp_processor_id();
 116
 117        /*
 118         * Select completion CPU
 119         */
 120        if (req->cpu != -1) {
 121                ccpu = req->cpu;
 122                if (!test_bit(QUEUE_FLAG_SAME_FORCE, &q->queue_flags))
 123                        shared = cpus_share_cache(cpu, ccpu);
 124        } else
 125                ccpu = cpu;
 126
 127        /*
 128         * If current CPU and requested CPU share a cache, run the softirq on
 129         * the current CPU. One might concern this is just like
 130         * QUEUE_FLAG_SAME_FORCE, but actually not. blk_complete_request() is
 131         * running in interrupt handler, and currently I/O controller doesn't
 132         * support multiple interrupts, so current CPU is unique actually. This
 133         * avoids IPI sending from current CPU to the first CPU of a group.
 134         */
 135        if (ccpu == cpu || shared) {
 136                struct list_head *list;
 137do_local:
 138                list = &__get_cpu_var(blk_cpu_done);
 139                list_add_tail(&req->csd.list, list);
 140
 141                /*
 142                 * if the list only contains our just added request,
 143                 * signal a raise of the softirq. If there are already
 144                 * entries there, someone already raised the irq but it
 145                 * hasn't run yet.
 146                 */
 147                if (list->next == &req->csd.list)
 148                        raise_softirq_irqoff(BLOCK_SOFTIRQ);
 149        } else if (raise_blk_irq(ccpu, req))
 150                goto do_local;
 151
 152        local_irq_restore(flags);
 153}
 154
 155/**
 156 * blk_complete_request - end I/O on a request
 157 * @req:      the request being processed
 158 *
 159 * Description:
 160 *     Ends all I/O on a request. It does not handle partial completions,
 161 *     unless the driver actually implements this in its completion callback
 162 *     through requeueing. The actual completion happens out-of-order,
 163 *     through a softirq handler. The user must have registered a completion
 164 *     callback through blk_queue_softirq_done().
 165 **/
 166void blk_complete_request(struct request *req)
 167{
 168        if (unlikely(blk_should_fake_timeout(req->q)))
 169                return;
 170        if (!blk_mark_rq_complete(req))
 171                __blk_complete_request(req);
 172}
 173EXPORT_SYMBOL(blk_complete_request);
 174
 175static __init int blk_softirq_init(void)
 176{
 177        int i;
 178
 179        for_each_possible_cpu(i)
 180                INIT_LIST_HEAD(&per_cpu(blk_cpu_done, i));
 181
 182        open_softirq(BLOCK_SOFTIRQ, blk_done_softirq);
 183        register_hotcpu_notifier(&blk_cpu_notifier);
 184        return 0;
 185}
 186subsys_initcall(blk_softirq_init);
 187
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