block: fix long lines in block/blk-iopoll.c
[linux-2.6.git] / 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
17 int blk_iopoll_enabled = 1;
18 EXPORT_SYMBOL(blk_iopoll_enabled);
19
20 static DEFINE_PER_CPU(struct list_head, blk_cpu_iopoll);
21
22 /**
23  * blk_iopoll_sched - Schedule a run of the iopoll handler
24  * @iop:      The parent iopoll structure
25  *
26  * Description:
27  *     Add this blk_iopoll structure to the pending poll list and trigger the
28  *     raise of the blk iopoll softirq. The driver must already have gotten a
29  *     succesful return from blk_iopoll_sched_prep() before calling this.
30  **/
31 void blk_iopoll_sched(struct blk_iopoll *iop)
32 {
33         unsigned long flags;
34
35         local_irq_save(flags);
36         list_add_tail(&iop->list, &__get_cpu_var(blk_cpu_iopoll));
37         __raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
38         local_irq_restore(flags);
39 }
40 EXPORT_SYMBOL(blk_iopoll_sched);
41
42 /**
43  * __blk_iopoll_complete - Mark this @iop as un-polled again
44  * @iop:      The parent iopoll structure
45  *
46  * Description:
47  *     See blk_iopoll_complete(). This function must be called with interrupts
48  *     disabled.
49  **/
50 void __blk_iopoll_complete(struct blk_iopoll *iop)
51 {
52         list_del(&iop->list);
53         smp_mb__before_clear_bit();
54         clear_bit_unlock(IOPOLL_F_SCHED, &iop->state);
55 }
56 EXPORT_SYMBOL(__blk_iopoll_complete);
57
58 /**
59  * blk_iopoll_complete - Mark this @iop as un-polled again
60  * @iop:      The parent iopoll structure
61  *
62  * Description:
63  *     If a driver consumes less than the assigned budget in its run of the
64  *     iopoll handler, it'll end the polled mode by calling this function. The
65  *     iopoll handler will not be invoked again before blk_iopoll_sched_prep()
66  *     is called.
67  **/
68 void blk_iopoll_complete(struct blk_iopoll *iopoll)
69 {
70         unsigned long flags;
71
72         local_irq_save(flags);
73         __blk_iopoll_complete(iopoll);
74         local_irq_restore(flags);
75 }
76 EXPORT_SYMBOL(blk_iopoll_complete);
77
78 static void blk_iopoll_softirq(struct softirq_action *h)
79 {
80         struct list_head *list = &__get_cpu_var(blk_cpu_iopoll);
81         unsigned long start_time = jiffies;
82         int rearm = 0, budget = 64;
83
84         local_irq_disable();
85
86         while (!list_empty(list)) {
87                 struct blk_iopoll *iop;
88                 int work, weight;
89
90                 /*
91                  * If softirq window is exhausted then punt.
92                  */
93                 if (budget <= 0 || time_after(jiffies, start_time)) {
94                         rearm = 1;
95                         break;
96                 }
97
98                 local_irq_enable();
99
100                 /* Even though interrupts have been re-enabled, this
101                  * access is safe because interrupts can only add new
102                  * entries to the tail of this list, and only ->poll()
103                  * calls can remove this head entry from the list.
104                  */
105                 iop = list_entry(list->next, struct blk_iopoll, list);
106
107                 weight = iop->weight;
108                 work = 0;
109                 if (test_bit(IOPOLL_F_SCHED, &iop->state))
110                         work = iop->poll(iop, weight);
111
112                 budget -= work;
113
114                 local_irq_disable();
115
116                 /* Drivers must not modify the NAPI state if they
117                  * consume the entire weight.  In such cases this code
118                  * still "owns" the NAPI instance and therefore can
119                  * move the instance around on the list at-will.
120                  */
121                 if (work >= weight) {
122                         if (blk_iopoll_disable_pending(iop))
123                                 __blk_iopoll_complete(iop);
124                         else
125                                 list_move_tail(&iop->list, list);
126                 }
127         }
128
129         if (rearm)
130                 __raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
131
132         local_irq_enable();
133 }
134
135 /**
136  * blk_iopoll_disable - Disable iopoll on this @iop
137  * @iop:      The parent iopoll structure
138  *
139  * Description:
140  *     Disable io polling and wait for any pending callbacks to have completed.
141  **/
142 void blk_iopoll_disable(struct blk_iopoll *iop)
143 {
144         set_bit(IOPOLL_F_DISABLE, &iop->state);
145         while (test_and_set_bit(IOPOLL_F_SCHED, &iop->state))
146                 msleep(1);
147         clear_bit(IOPOLL_F_DISABLE, &iop->state);
148 }
149 EXPORT_SYMBOL(blk_iopoll_disable);
150
151 /**
152  * blk_iopoll_enable - Enable iopoll on this @iop
153  * @iop:      The parent iopoll structure
154  *
155  * Description:
156  *     Enable iopoll on this @iop. Note that the handler run will not be
157  *     scheduled, it will only mark it as active.
158  **/
159 void blk_iopoll_enable(struct blk_iopoll *iop)
160 {
161         BUG_ON(!test_bit(IOPOLL_F_SCHED, &iop->state));
162         smp_mb__before_clear_bit();
163         clear_bit_unlock(IOPOLL_F_SCHED, &iop->state);
164 }
165 EXPORT_SYMBOL(blk_iopoll_enable);
166
167 /**
168  * blk_iopoll_init - Initialize this @iop
169  * @iop:      The parent iopoll structure
170  * @weight:   The default weight (or command completion budget)
171  * @poll_fn:  The handler to invoke
172  *
173  * Description:
174  *     Initialize this blk_iopoll structure. Before being actively used, the
175  *     driver must call blk_iopoll_enable().
176  **/
177 void blk_iopoll_init(struct blk_iopoll *iop, int weight, blk_iopoll_fn *poll_fn)
178 {
179         memset(iop, 0, sizeof(*iop));
180         INIT_LIST_HEAD(&iop->list);
181         iop->weight = weight;
182         iop->poll = poll_fn;
183         set_bit(IOPOLL_F_SCHED, &iop->state);
184 }
185 EXPORT_SYMBOL(blk_iopoll_init);
186
187 static int __cpuinit blk_iopoll_cpu_notify(struct notifier_block *self,
188                                           unsigned long action, void *hcpu)
189 {
190         /*
191          * If a CPU goes away, splice its entries to the current CPU
192          * and trigger a run of the softirq
193          */
194         if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
195                 int cpu = (unsigned long) hcpu;
196
197                 local_irq_disable();
198                 list_splice_init(&per_cpu(blk_cpu_iopoll, cpu),
199                                  &__get_cpu_var(blk_cpu_iopoll));
200                 raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
201                 local_irq_enable();
202         }
203
204         return NOTIFY_OK;
205 }
206
207 static struct notifier_block __cpuinitdata blk_iopoll_cpu_notifier = {
208         .notifier_call  = blk_iopoll_cpu_notify,
209 };
210
211 static __init int blk_iopoll_setup(void)
212 {
213         int i;
214
215         for_each_possible_cpu(i)
216                 INIT_LIST_HEAD(&per_cpu(blk_cpu_iopoll, i));
217
218         open_softirq(BLOCK_IOPOLL_SOFTIRQ, blk_iopoll_softirq);
219         register_hotcpu_notifier(&blk_iopoll_cpu_notifier);
220         return 0;
221 }
222 subsys_initcall(blk_iopoll_setup);