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, queuelist);
  34                 list_del_init(&rq->queuelist);
  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         /*
  49          * We reuse queuelist for a list of requests to process. Since the
  50          * queuelist is used by the block layer only for requests waiting to be
  51          * submitted to the device it is unused now.
  52          */
  53         list_add_tail(&rq->queuelist, list);
  54
  55         if (list->next == &rq->queuelist)
  56                 raise_softirq_irqoff(BLOCK_SOFTIRQ);
  57
  58         local_irq_restore(flags);
  59 }
  60
  61 /*
  62  * Setup and invoke a run of 'trigger_softirq' on the given cpu.
  63  */
  64 static int raise_blk_irq(int cpu, struct request *rq)
  65 {
  66         if (cpu_online(cpu)) {
  67                 struct call_single_data *data = &rq->csd;
  68
  69                 data->func = trigger_softirq;
  70                 data->info = rq;
  71                 data->flags = 0;
  72
  73                 smp_call_function_single_async(cpu, data);
  74                 return 0;
  75         }
  76
  77         return 1;
  78 }
  79 #else /* CONFIG_SMP */
  80 static int raise_blk_irq(int cpu, struct request *rq)
  81 {
  82         return 1;
  83 }
  84 #endif
  85
  86 static int blk_cpu_notify(struct notifier_block *self, unsigned long action,
  87                           void *hcpu)
  88 {
  89         /*
  90          * If a CPU goes away, splice its entries to the current CPU
  91          * and trigger a run of the softirq
  92          */
  93         if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
  94                 int cpu = (unsigned long) hcpu;
  95
  96                 local_irq_disable();
  97                 list_splice_init(&per_cpu(blk_cpu_done, cpu),
  98                                  this_cpu_ptr(&blk_cpu_done));
  99                 raise_softirq_irqoff(BLOCK_SOFTIRQ);
 100                 local_irq_enable();
 101         }
 102
 103         return NOTIFY_OK;
 104 }
 105
 106 static struct notifier_block blk_cpu_notifier = {
 107         .notifier_call  = blk_cpu_notify,
 108 };
 109
 110 void __blk_complete_request(struct request *req)
 111 {
 112         int ccpu, cpu;
 113         struct request_queue *q = req->q;
 114         unsigned long flags;
 115         bool shared = false;
 116
 117         BUG_ON(!q->softirq_done_fn);
 118
 119         local_irq_save(flags);
 120         cpu = smp_processor_id();
 121
 122         /*
 123          * Select completion CPU
 124          */
 125         if (req->cpu != -1) {
 126                 ccpu = req->cpu;
 127                 if (!test_bit(QUEUE_FLAG_SAME_FORCE, &q->queue_flags))
 128                         shared = cpus_share_cache(cpu, ccpu);
 129         } else
 130                 ccpu = cpu;
 131
 132         /*
 133          * If current CPU and requested CPU share a cache, run the softirq on
 134          * the current CPU. One might concern this is just like
 135          * QUEUE_FLAG_SAME_FORCE, but actually not. blk_complete_request() is
 136          * running in interrupt handler, and currently I/O controller doesn't
 137          * support multiple interrupts, so current CPU is unique actually. This
 138          * avoids IPI sending from current CPU to the first CPU of a group.
 139          */
 140         if (ccpu == cpu || shared) {
 141                 struct list_head *list;
 142 do_local:
 143                 list = this_cpu_ptr(&blk_cpu_done);
 144                 list_add_tail(&req->queuelist, list);
 145
 146                 /*
 147                  * if the list only contains our just added request,
 148                  * signal a raise of the softirq. If there are already
 149                  * entries there, someone already raised the irq but it
 150                  * hasn't run yet.
 151                  */
 152                 if (list->next == &req->queuelist)
 153                         raise_softirq_irqoff(BLOCK_SOFTIRQ);
 154         } else if (raise_blk_irq(ccpu, req))
 155                 goto do_local;
 156
 157         local_irq_restore(flags);
 158 }
 159
 160 /**
 161  * blk_complete_request - end I/O on a request
 162  * @req:      the request being processed
 163  *
 164  * Description:
 165  *     Ends all I/O on a request. It does not handle partial completions,
 166  *     unless the driver actually implements this in its completion callback
 167  *     through requeueing. The actual completion happens out-of-order,
 168  *     through a softirq handler. The user must have registered a completion
 169  *     callback through blk_queue_softirq_done().
 170  **/
 171 void blk_complete_request(struct request *req)
 172 {
 173         if (unlikely(blk_should_fake_timeout(req->q)))
 174                 return;
 175         if (!blk_mark_rq_complete(req))
 176                 __blk_complete_request(req);
 177 }
 178 EXPORT_SYMBOL(blk_complete_request);
 179
 180 static __init int blk_softirq_init(void)
 181 {
 182         int i;
 183
 184         for_each_possible_cpu(i)
 185                 INIT_LIST_HEAD(&per_cpu(blk_cpu_done, i));
 186
 187         open_softirq(BLOCK_SOFTIRQ, blk_done_softirq);
 188         register_hotcpu_notifier(&blk_cpu_notifier);
 189         return 0;
 190 }
 191 subsys_initcall(blk_softirq_init);