block/blk-softirq.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Functions related to softirq rq completions
   4  */
   5 #include <linux/kernel.h>
   6 #include <linux/module.h>
   7 #include <linux/init.h>
   8 #include <linux/bio.h>
   9 #include <linux/blkdev.h>
  10 #include <linux/interrupt.h>
  11 #include <linux/cpu.h>
  12 #include <linux/sched.h>
  13 #include <linux/sched/topology.h>
  14
  15 #include "blk.h"
  16
  17 static DEFINE_PER_CPU(struct list_head, blk_cpu_done);
  18
  19 /*
  20  * Softirq action handler - move entries to local list and loop over them
  21  * while passing them to the queue registered handler.
  22  */
  23 static __latent_entropy void blk_done_softirq(struct softirq_action *h)
  24 {
  25         struct list_head *cpu_list, local_list;
  26
  27         local_irq_disable();
  28         cpu_list = this_cpu_ptr(&blk_cpu_done);
  29         list_replace_init(cpu_list, &local_list);
  30         local_irq_enable();
  31
  32         while (!list_empty(&local_list)) {
  33                 struct request *rq;
  34
  35                 rq = list_entry(local_list.next, struct request, ipi_list);
  36                 list_del_init(&rq->ipi_list);
  37                 rq->q->mq_ops->complete(rq);
  38         }
  39 }
  40
  41 #ifdef CONFIG_SMP
  42 static void trigger_softirq(void *data)
  43 {
  44         struct request *rq = data;
  45         struct list_head *list;
  46
  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
  54 /*
  55  * Setup and invoke a run of 'trigger_softirq' on the given cpu.
  56  */
  57 static int raise_blk_irq(int cpu, struct request *rq)
  58 {
  59         if (cpu_online(cpu)) {
  60                 call_single_data_t *data = &rq->csd;
  61
  62                 data->func = trigger_softirq;
  63                 data->info = rq;
  64                 data->flags = 0;
  65
  66                 smp_call_function_single_async(cpu, data);
  67                 return 0;
  68         }
  69
  70         return 1;
  71 }
  72 #else /* CONFIG_SMP */
  73 static int raise_blk_irq(int cpu, struct request *rq)
  74 {
  75         return 1;
  76 }
  77 #endif
  78
  79 static int blk_softirq_cpu_dead(unsigned int cpu)
  80 {
  81         /*
  82          * If a CPU goes away, splice its entries to the current CPU
  83          * and trigger a run of the softirq
  84          */
  85         local_irq_disable();
  86         list_splice_init(&per_cpu(blk_cpu_done, cpu),
  87                          this_cpu_ptr(&blk_cpu_done));
  88         raise_softirq_irqoff(BLOCK_SOFTIRQ);
  89         local_irq_enable();
  90
  91         return 0;
  92 }
  93
  94 void __blk_complete_request(struct request *req)
  95 {
  96         struct request_queue *q = req->q;
  97         int cpu, ccpu = req->mq_ctx->cpu;
  98         unsigned long flags;
  99         bool shared = false;
 100
 101         BUG_ON(!q->mq_ops->complete);
 102
 103         local_irq_save(flags);
 104         cpu = smp_processor_id();
 105
 106         /*
 107          * Select completion CPU
 108          */
 109         if (test_bit(QUEUE_FLAG_SAME_COMP, &q->queue_flags) && ccpu != -1) {
 110                 if (!test_bit(QUEUE_FLAG_SAME_FORCE, &q->queue_flags))
 111                         shared = cpus_share_cache(cpu, ccpu);
 112         } else
 113                 ccpu = cpu;
 114
 115         /*
 116          * If current CPU and requested CPU share a cache, run the softirq on
 117          * the current CPU. One might concern this is just like
 118          * QUEUE_FLAG_SAME_FORCE, but actually not. blk_complete_request() is
 119          * running in interrupt handler, and currently I/O controller doesn't
 120          * support multiple interrupts, so current CPU is unique actually. This
 121          * avoids IPI sending from current CPU to the first CPU of a group.
 122          */
 123         if (ccpu == cpu || shared) {
 124                 struct list_head *list;
 125 do_local:
 126                 list = this_cpu_ptr(&blk_cpu_done);
 127                 list_add_tail(&req->ipi_list, list);
 128
 129                 /*
 130                  * if the list only contains our just added request,
 131                  * signal a raise of the softirq. If there are already
 132                  * entries there, someone already raised the irq but it
 133                  * hasn't run yet.
 134                  */
 135                 if (list->next == &req->ipi_list)
 136                         raise_softirq_irqoff(BLOCK_SOFTIRQ);
 137         } else if (raise_blk_irq(ccpu, req))
 138                 goto do_local;
 139
 140         local_irq_restore(flags);
 141 }
 142
 143 static __init int blk_softirq_init(void)
 144 {
 145         int i;
 146
 147         for_each_possible_cpu(i)
 148                 INIT_LIST_HEAD(&per_cpu(blk_cpu_done, i));
 149
 150         open_softirq(BLOCK_SOFTIRQ, blk_done_softirq);
 151         cpuhp_setup_state_nocalls(CPUHP_BLOCK_SOFTIRQ_DEAD,
 152                                   "block/softirq:dead", NULL,
 153                                   blk_softirq_cpu_dead);
 154         return 0;
 155 }
 156 subsys_initcall(blk_softirq_init);