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5e605b64 »
2009-08-05 block: add blk-iopoll, a NAPI like approach for block devices
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
17 int blk_iopoll_enabled = 1;
18 EXPORT_SYMBOL(blk_iopoll_enabled);
19
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2009-08-06 block: adjust default budget for blk-iopoll
20 static unsigned int blk_iopoll_budget __read_mostly = 256;
21
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2009-08-05 block: add blk-iopoll, a NAPI like approach for block devices
22 static 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:
1badcfbd »
2009-08-06 block: fix long lines in block/blk-iopoll.c
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
af901ca1 »
2009-11-14 tree-wide: fix assorted typos all over the place
31 * successful return from blk_iopoll_sched_prep() before calling this.
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2009-08-05 block: add blk-iopoll, a NAPI like approach for block devices
32 **/
33 void 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 }
42 EXPORT_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:
1badcfbd »
2009-08-06 block: fix long lines in block/blk-iopoll.c
49 * See blk_iopoll_complete(). This function must be called with interrupts
50 * disabled.
5e605b64 »
2009-08-05 block: add blk-iopoll, a NAPI like approach for block devices
51 **/
52 void __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 }
58 EXPORT_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:
1badcfbd »
2009-08-06 block: fix long lines in block/blk-iopoll.c
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.
5e605b64 »
2009-08-05 block: add blk-iopoll, a NAPI like approach for block devices
69 **/
70 void 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 }
78 EXPORT_SYMBOL(blk_iopoll_complete);
79
80 static void blk_iopoll_softirq(struct softirq_action *h)
81 {
82 struct list_head *list = &__get_cpu_var(blk_cpu_iopoll);
37867ae7 »
2009-08-06 block: adjust default budget for blk-iopoll
83 int rearm = 0, budget = blk_iopoll_budget;
5e605b64 »
2009-08-05 block: add blk-iopoll, a NAPI like approach for block devices
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
fca51d64 »
2009-08-06 block: fix comment in blk-iopoll.c
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
5e605b64 »
2009-08-05 block: add blk-iopoll, a NAPI like approach for block devices
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 **/
147 void 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 }
154 EXPORT_SYMBOL(blk_iopoll_disable);
155
156 /**
157 * blk_iopoll_enable - Enable iopoll on this @iop
158 * @iop: The parent iopoll structure
159 *
160 * Description:
1badcfbd »
2009-08-06 block: fix long lines in block/blk-iopoll.c
161 * Enable iopoll on this @iop. Note that the handler run will not be
162 * scheduled, it will only mark it as active.
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2009-08-05 block: add blk-iopoll, a NAPI like approach for block devices
163 **/
164 void blk_iopoll_enable(struct blk_iopoll *iop)
165 {
166 BUG_ON(!test_bit(IOPOLL_F_SCHED, &iop->state));
1badcfbd »
2009-08-06 block: fix long lines in block/blk-iopoll.c
167 smp_mb__before_clear_bit();
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2009-08-05 block: add blk-iopoll, a NAPI like approach for block devices
168 clear_bit_unlock(IOPOLL_F_SCHED, &iop->state);
169 }
170 EXPORT_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:
1badcfbd »
2009-08-06 block: fix long lines in block/blk-iopoll.c
179 * Initialize this blk_iopoll structure. Before being actively used, the
180 * driver must call blk_iopoll_enable().
5e605b64 »
2009-08-05 block: add blk-iopoll, a NAPI like approach for block devices
181 **/
182 void 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 }
190 EXPORT_SYMBOL(blk_iopoll_init);
191
192 static 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));
a33dac26 »
2009-08-06 block: use interrupts disabled version of raise_softirq_irqoff()
205 __raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
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2009-08-05 block: add blk-iopoll, a NAPI like approach for block devices
206 local_irq_enable();
207 }
208
209 return NOTIFY_OK;
210 }
211
212 static struct notifier_block __cpuinitdata blk_iopoll_cpu_notifier = {
213 .notifier_call = blk_iopoll_cpu_notify,
214 };
215
216 static __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 }
227 subsys_initcall(blk_iopoll_setup);
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