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TOMOYO Linux Cross Reference
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 
 12 #include "blk.h"
 13 
 14 static DEFINE_PER_CPU(struct list_head, blk_cpu_done);
 15 
 16 /*
 17  * Softirq action handler - move entries to local list and loop over them
 18  * while passing them to the queue registered handler.
 19  */
 20 static void blk_done_softirq(struct softirq_action *h)
 21 {
 22         struct list_head *cpu_list, local_list;
 23 
 24         local_irq_disable();
 25         cpu_list = &__get_cpu_var(blk_cpu_done);
 26         list_replace_init(cpu_list, &local_list);
 27         local_irq_enable();
 28 
 29         while (!list_empty(&local_list)) {
 30                 struct request *rq;
 31 
 32                 rq = list_entry(local_list.next, struct request, csd.list);
 33                 list_del_init(&rq->csd.list);
 34                 rq->q->softirq_done_fn(rq);
 35         }
 36 }
 37 
 38 #if defined(CONFIG_SMP) && defined(CONFIG_USE_GENERIC_SMP_HELPERS)
 39 static void trigger_softirq(void *data)
 40 {
 41         struct request *rq = data;
 42         unsigned long flags;
 43         struct list_head *list;
 44 
 45         local_irq_save(flags);
 46         list = &__get_cpu_var(blk_cpu_done);
 47         list_add_tail(&rq->csd.list, list);
 48 
 49         if (list->next == &rq->csd.list)
 50                 raise_softirq_irqoff(BLOCK_SOFTIRQ);
 51 
 52         local_irq_restore(flags);
 53 }
 54 
 55 /*
 56  * Setup and invoke a run of 'trigger_softirq' on the given cpu.
 57  */
 58 static int raise_blk_irq(int cpu, struct request *rq)
 59 {
 60         if (cpu_online(cpu)) {
 61                 struct call_single_data *data = &rq->csd;
 62 
 63                 data->func = trigger_softirq;
 64                 data->info = rq;
 65                 data->flags = 0;
 66 
 67                 __smp_call_function_single(cpu, data, 0);
 68                 return 0;
 69         }
 70 
 71         return 1;
 72 }
 73 #else /* CONFIG_SMP && CONFIG_USE_GENERIC_SMP_HELPERS */
 74 static int raise_blk_irq(int cpu, struct request *rq)
 75 {
 76         return 1;
 77 }
 78 #endif
 79 
 80 static int __cpuinit blk_cpu_notify(struct notifier_block *self,
 81                                     unsigned long action, void *hcpu)
 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         if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
 88                 int cpu = (unsigned long) hcpu;
 89 
 90                 local_irq_disable();
 91                 list_splice_init(&per_cpu(blk_cpu_done, cpu),
 92                                  &__get_cpu_var(blk_cpu_done));
 93                 raise_softirq_irqoff(BLOCK_SOFTIRQ);
 94                 local_irq_enable();
 95         }
 96 
 97         return NOTIFY_OK;
 98 }
 99 
100 static struct notifier_block __cpuinitdata blk_cpu_notifier = {
101         .notifier_call  = blk_cpu_notify,
102 };
103 
104 void __blk_complete_request(struct request *req)
105 {
106         int ccpu, cpu, group_cpu = NR_CPUS;
107         struct request_queue *q = req->q;
108         unsigned long flags;
109 
110         BUG_ON(!q->softirq_done_fn);
111 
112         local_irq_save(flags);
113         cpu = smp_processor_id();
114 
115         /*
116          * Select completion CPU
117          */
118         if (req->cpu != -1) {
119                 ccpu = req->cpu;
120                 if (!test_bit(QUEUE_FLAG_SAME_FORCE, &q->queue_flags)) {
121                         ccpu = blk_cpu_to_group(ccpu);
122                         group_cpu = blk_cpu_to_group(cpu);
123                 }
124         } else
125                 ccpu = cpu;
126 
127         /*
128          * If current CPU and requested CPU are in the same group, running
129          * softirq in 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 || ccpu == group_cpu) {
136                 struct list_head *list;
137 do_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  **/
166 void 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 }
173 EXPORT_SYMBOL(blk_complete_request);
174 
175 static __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 }
186 subsys_initcall(blk_softirq_init);
187 

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