Root/block/blk-iopoll.c

1/*
2 * Functions related to interrupt-poll handling in the block layer. This
3 * is similar to NAPI for network devices.
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/blk-iopoll.h>
13#include <linux/delay.h>
14
15#include "blk.h"
16
17int blk_iopoll_enabled = 1;
18EXPORT_SYMBOL(blk_iopoll_enabled);
19
20static unsigned int blk_iopoll_budget __read_mostly = 256;
21
22static DEFINE_PER_CPU(struct list_head, blk_cpu_iopoll);
23
24/**
25 * blk_iopoll_sched - Schedule a run of the iopoll handler
26 * @iop: The parent iopoll structure
27 *
28 * Description:
29 * Add this blk_iopoll structure to the pending poll list and trigger the
30 * raise of the blk iopoll softirq. The driver must already have gotten a
31 * succesful return from blk_iopoll_sched_prep() before calling this.
32 **/
33void blk_iopoll_sched(struct blk_iopoll *iop)
34{
35    unsigned long flags;
36
37    local_irq_save(flags);
38    list_add_tail(&iop->list, &__get_cpu_var(blk_cpu_iopoll));
39    __raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
40    local_irq_restore(flags);
41}
42EXPORT_SYMBOL(blk_iopoll_sched);
43
44/**
45 * __blk_iopoll_complete - Mark this @iop as un-polled again
46 * @iop: The parent iopoll structure
47 *
48 * Description:
49 * See blk_iopoll_complete(). This function must be called with interrupts
50 * disabled.
51 **/
52void __blk_iopoll_complete(struct blk_iopoll *iop)
53{
54    list_del(&iop->list);
55    smp_mb__before_clear_bit();
56    clear_bit_unlock(IOPOLL_F_SCHED, &iop->state);
57}
58EXPORT_SYMBOL(__blk_iopoll_complete);
59
60/**
61 * blk_iopoll_complete - Mark this @iop as un-polled again
62 * @iop: The parent iopoll structure
63 *
64 * Description:
65 * If a driver consumes less than the assigned budget in its run of the
66 * iopoll handler, it'll end the polled mode by calling this function. The
67 * iopoll handler will not be invoked again before blk_iopoll_sched_prep()
68 * is called.
69 **/
70void blk_iopoll_complete(struct blk_iopoll *iopoll)
71{
72    unsigned long flags;
73
74    local_irq_save(flags);
75    __blk_iopoll_complete(iopoll);
76    local_irq_restore(flags);
77}
78EXPORT_SYMBOL(blk_iopoll_complete);
79
80static void blk_iopoll_softirq(struct softirq_action *h)
81{
82    struct list_head *list = &__get_cpu_var(blk_cpu_iopoll);
83    int rearm = 0, budget = blk_iopoll_budget;
84    unsigned long start_time = jiffies;
85
86    local_irq_disable();
87
88    while (!list_empty(list)) {
89        struct blk_iopoll *iop;
90        int work, weight;
91
92        /*
93         * If softirq window is exhausted then punt.
94         */
95        if (budget <= 0 || time_after(jiffies, start_time)) {
96            rearm = 1;
97            break;
98        }
99
100        local_irq_enable();
101
102        /* Even though interrupts have been re-enabled, this
103         * access is safe because interrupts can only add new
104         * entries to the tail of this list, and only ->poll()
105         * calls can remove this head entry from the list.
106         */
107        iop = list_entry(list->next, struct blk_iopoll, list);
108
109        weight = iop->weight;
110        work = 0;
111        if (test_bit(IOPOLL_F_SCHED, &iop->state))
112            work = iop->poll(iop, weight);
113
114        budget -= work;
115
116        local_irq_disable();
117
118        /*
119         * Drivers must not modify the iopoll state, if they
120         * consume their assigned weight (or more, some drivers can't
121         * easily just stop processing, they have to complete an
122         * entire mask of commands).In such cases this code
123         * still "owns" the iopoll instance and therefore can
124         * move the instance around on the list at-will.
125         */
126        if (work >= weight) {
127            if (blk_iopoll_disable_pending(iop))
128                __blk_iopoll_complete(iop);
129            else
130                list_move_tail(&iop->list, list);
131        }
132    }
133
134    if (rearm)
135        __raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
136
137    local_irq_enable();
138}
139
140/**
141 * blk_iopoll_disable - Disable iopoll on this @iop
142 * @iop: The parent iopoll structure
143 *
144 * Description:
145 * Disable io polling and wait for any pending callbacks to have completed.
146 **/
147void blk_iopoll_disable(struct blk_iopoll *iop)
148{
149    set_bit(IOPOLL_F_DISABLE, &iop->state);
150    while (test_and_set_bit(IOPOLL_F_SCHED, &iop->state))
151        msleep(1);
152    clear_bit(IOPOLL_F_DISABLE, &iop->state);
153}
154EXPORT_SYMBOL(blk_iopoll_disable);
155
156/**
157 * blk_iopoll_enable - Enable iopoll on this @iop
158 * @iop: The parent iopoll structure
159 *
160 * Description:
161 * Enable iopoll on this @iop. Note that the handler run will not be
162 * scheduled, it will only mark it as active.
163 **/
164void blk_iopoll_enable(struct blk_iopoll *iop)
165{
166    BUG_ON(!test_bit(IOPOLL_F_SCHED, &iop->state));
167    smp_mb__before_clear_bit();
168    clear_bit_unlock(IOPOLL_F_SCHED, &iop->state);
169}
170EXPORT_SYMBOL(blk_iopoll_enable);
171
172/**
173 * blk_iopoll_init - Initialize this @iop
174 * @iop: The parent iopoll structure
175 * @weight: The default weight (or command completion budget)
176 * @poll_fn: The handler to invoke
177 *
178 * Description:
179 * Initialize this blk_iopoll structure. Before being actively used, the
180 * driver must call blk_iopoll_enable().
181 **/
182void blk_iopoll_init(struct blk_iopoll *iop, int weight, blk_iopoll_fn *poll_fn)
183{
184    memset(iop, 0, sizeof(*iop));
185    INIT_LIST_HEAD(&iop->list);
186    iop->weight = weight;
187    iop->poll = poll_fn;
188    set_bit(IOPOLL_F_SCHED, &iop->state);
189}
190EXPORT_SYMBOL(blk_iopoll_init);
191
192static int __cpuinit blk_iopoll_cpu_notify(struct notifier_block *self,
193                      unsigned long action, void *hcpu)
194{
195    /*
196     * If a CPU goes away, splice its entries to the current CPU
197     * and trigger a run of the softirq
198     */
199    if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
200        int cpu = (unsigned long) hcpu;
201
202        local_irq_disable();
203        list_splice_init(&per_cpu(blk_cpu_iopoll, cpu),
204                 &__get_cpu_var(blk_cpu_iopoll));
205        __raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
206        local_irq_enable();
207    }
208
209    return NOTIFY_OK;
210}
211
212static struct notifier_block __cpuinitdata blk_iopoll_cpu_notifier = {
213    .notifier_call = blk_iopoll_cpu_notify,
214};
215
216static __init int blk_iopoll_setup(void)
217{
218    int i;
219
220    for_each_possible_cpu(i)
221        INIT_LIST_HEAD(&per_cpu(blk_cpu_iopoll, i));
222
223    open_softirq(BLOCK_IOPOLL_SOFTIRQ, blk_iopoll_softirq);
224    register_hotcpu_notifier(&blk_iopoll_cpu_notifier);
225    return 0;
226}
227subsys_initcall(blk_iopoll_setup);
228

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