block: add support for IO CPU affinity
[linux-2.6.git] / 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
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);
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 /**
105  * blk_complete_request - end I/O on a request
106  * @req:      the request being processed
107  *
108  * Description:
109  *     Ends all I/O on a request. It does not handle partial completions,
110  *     unless the driver actually implements this in its completion callback
111  *     through requeueing. The actual completion happens out-of-order,
112  *     through a softirq handler. The user must have registered a completion
113  *     callback through blk_queue_softirq_done().
114  **/
115 void blk_complete_request(struct request *req)
116 {
117         struct request_queue *q = req->q;
118         unsigned long flags;
119         int ccpu, cpu, group_cpu;
120
121         BUG_ON(!q->softirq_done_fn);
122
123         local_irq_save(flags);
124         cpu = smp_processor_id();
125         group_cpu = blk_cpu_to_group(cpu);
126
127         /*
128          * Select completion CPU
129          */
130         if (test_bit(QUEUE_FLAG_SAME_COMP, &q->queue_flags) && req->cpu != -1)
131                 ccpu = req->cpu;
132         else
133                 ccpu = cpu;
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 EXPORT_SYMBOL(blk_complete_request);
155
156 __init int blk_softirq_init(void)
157 {
158         int i;
159
160         for_each_possible_cpu(i)
161                 INIT_LIST_HEAD(&per_cpu(blk_cpu_done, i));
162
163         open_softirq(BLOCK_SOFTIRQ, blk_done_softirq);
164         register_hotcpu_notifier(&blk_cpu_notifier);
165         return 0;
166 }
167 subsys_initcall(blk_softirq_init);