kernel/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
  15 static 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  */
  21 static 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
  40 static 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         preempt_check_resched_rt();
  55 }
  56
  57 /*
  58  * Setup and invoke a run of 'trigger_softirq' on the given cpu.
  59  */
  60 static int raise_blk_irq(int cpu, struct request *rq)
  61 {
  62         if (cpu_online(cpu)) {
  63                 struct call_single_data *data = &rq->csd;
  64
  65                 data->func = trigger_softirq;
  66                 data->info = rq;
  67                 data->flags = 0;
  68
  69                 smp_call_function_single_async(cpu, data);
  70                 return 0;
  71         }
  72
  73         return 1;
  74 }
  75 #else /* CONFIG_SMP */
  76 static int raise_blk_irq(int cpu, struct request *rq)
  77 {
  78         return 1;
  79 }
  80 #endif
  81
  82 static int blk_cpu_notify(struct notifier_block *self, unsigned long action,
  83                           void *hcpu)
  84 {
  85         /*
  86          * If a CPU goes away, splice its entries to the current CPU
  87          * and trigger a run of the softirq
  88          */
  89         if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
  90                 int cpu = (unsigned long) hcpu;
  91
  92                 local_irq_disable();
  93                 list_splice_init(&per_cpu(blk_cpu_done, cpu),
  94                                  this_cpu_ptr(&blk_cpu_done));
  95                 raise_softirq_irqoff(BLOCK_SOFTIRQ);
  96                 local_irq_enable();
  97                 preempt_check_resched_rt();
  98         }
  99
 100         return NOTIFY_OK;
 101 }
 102
 103 static struct notifier_block blk_cpu_notifier = {
 104         .notifier_call  = blk_cpu_notify,
 105 };
 106
 107 void __blk_complete_request(struct request *req)
 108 {
 109         int ccpu, cpu;
 110         struct request_queue *q = req->q;
 111         unsigned long flags;
 112         bool shared = false;
 113
 114         BUG_ON(!q->softirq_done_fn);
 115
 116         local_irq_save(flags);
 117         cpu = smp_processor_id();
 118
 119         /*
 120          * Select completion CPU
 121          */
 122         if (req->cpu != -1) {
 123                 ccpu = req->cpu;
 124                 if (!test_bit(QUEUE_FLAG_SAME_FORCE, &q->queue_flags))
 125                         shared = cpus_share_cache(cpu, ccpu);
 126         } else
 127                 ccpu = cpu;
 128
 129         /*
 130          * If current CPU and requested CPU share a cache, run the softirq on
 131          * the current CPU. One might concern this is just like
 132          * QUEUE_FLAG_SAME_FORCE, but actually not. blk_complete_request() is
 133          * running in interrupt handler, and currently I/O controller doesn't
 134          * support multiple interrupts, so current CPU is unique actually. This
 135          * avoids IPI sending from current CPU to the first CPU of a group.
 136          */
 137         if (ccpu == cpu || shared) {
 138                 struct list_head *list;
 139 do_local:
 140                 list = this_cpu_ptr(&blk_cpu_done);
 141                 list_add_tail(&req->ipi_list, list);
 142
 143                 /*
 144                  * if the list only contains our just added request,
 145                  * signal a raise of the softirq. If there are already
 146                  * entries there, someone already raised the irq but it
 147                  * hasn't run yet.
 148                  */
 149                 if (list->next == &req->ipi_list)
 150                         raise_softirq_irqoff(BLOCK_SOFTIRQ);
 151         } else if (raise_blk_irq(ccpu, req))
 152                 goto do_local;
 153
 154         local_irq_restore(flags);
 155         preempt_check_resched_rt();
 156 }
 157
 158 /**
 159  * blk_complete_request - end I/O on a request
 160  * @req:      the request being processed
 161  *
 162  * Description:
 163  *     Ends all I/O on a request. It does not handle partial completions,
 164  *     unless the driver actually implements this in its completion callback
 165  *     through requeueing. The actual completion happens out-of-order,
 166  *     through a softirq handler. The user must have registered a completion
 167  *     callback through blk_queue_softirq_done().
 168  **/
 169 void blk_complete_request(struct request *req)
 170 {
 171         if (unlikely(blk_should_fake_timeout(req->q)))
 172                 return;
 173         if (!blk_mark_rq_complete(req))
 174                 __blk_complete_request(req);
 175 }
 176 EXPORT_SYMBOL(blk_complete_request);
 177
 178 static __init int blk_softirq_init(void)
 179 {
 180         int i;
 181
 182         for_each_possible_cpu(i)
 183                 INIT_LIST_HEAD(&per_cpu(blk_cpu_done, i));
 184
 185         open_softirq(BLOCK_SOFTIRQ, blk_done_softirq);
 186         register_hotcpu_notifier(&blk_cpu_notifier);
 187         return 0;
 188 }
 189 subsys_initcall(blk_softirq_init);