Root/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
15static 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 */
21static 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 = &__get_cpu_var(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, csd.list);
34        list_del_init(&rq->csd.list);
35        rq->q->softirq_done_fn(rq);
36    }
37}
38
39#if defined(CONFIG_SMP) && defined(CONFIG_USE_GENERIC_SMP_HELPERS)
40static 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 = &__get_cpu_var(blk_cpu_done);
48    list_add_tail(&rq->csd.list, list);
49
50    if (list->next == &rq->csd.list)
51        raise_softirq_irqoff(BLOCK_SOFTIRQ);
52
53    local_irq_restore(flags);
54}
55
56/*
57 * Setup and invoke a run of 'trigger_softirq' on the given cpu.
58 */
59static int raise_blk_irq(int cpu, struct request *rq)
60{
61    if (cpu_online(cpu)) {
62        struct call_single_data *data = &rq->csd;
63
64        data->func = trigger_softirq;
65        data->info = rq;
66        data->flags = 0;
67
68        __smp_call_function_single(cpu, data, 0);
69        return 0;
70    }
71
72    return 1;
73}
74#else /* CONFIG_SMP && CONFIG_USE_GENERIC_SMP_HELPERS */
75static int raise_blk_irq(int cpu, struct request *rq)
76{
77    return 1;
78}
79#endif
80
81static int __cpuinit blk_cpu_notify(struct notifier_block *self,
82                    unsigned long action, void *hcpu)
83{
84    /*
85     * If a CPU goes away, splice its entries to the current CPU
86     * and trigger a run of the softirq
87     */
88    if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
89        int cpu = (unsigned long) hcpu;
90
91        local_irq_disable();
92        list_splice_init(&per_cpu(blk_cpu_done, cpu),
93                 &__get_cpu_var(blk_cpu_done));
94        raise_softirq_irqoff(BLOCK_SOFTIRQ);
95        local_irq_enable();
96    }
97
98    return NOTIFY_OK;
99}
100
101static struct notifier_block __cpuinitdata blk_cpu_notifier = {
102    .notifier_call = blk_cpu_notify,
103};
104
105void __blk_complete_request(struct request *req)
106{
107    int ccpu, cpu;
108    struct request_queue *q = req->q;
109    unsigned long flags;
110    bool shared = false;
111
112    BUG_ON(!q->softirq_done_fn);
113
114    local_irq_save(flags);
115    cpu = smp_processor_id();
116
117    /*
118     * Select completion CPU
119     */
120    if (req->cpu != -1) {
121        ccpu = req->cpu;
122        if (!test_bit(QUEUE_FLAG_SAME_FORCE, &q->queue_flags))
123            shared = cpus_share_cache(cpu, ccpu);
124    } else
125        ccpu = cpu;
126
127    /*
128     * If current CPU and requested CPU share a cache, run the softirq on
129     * the 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 || shared) {
136        struct list_head *list;
137do_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 **/
166void 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}
173EXPORT_SYMBOL(blk_complete_request);
174
175static __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}
186subsys_initcall(blk_softirq_init);
187

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