2 * Functions related to interrupt-poll handling in the block layer. This
3 * is similar to NAPI for network devices.
5 #include <linux/kernel.h>
6 #include <linux/module.h>
7 #include <linux/init.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>
17 static unsigned int blk_iopoll_budget __read_mostly = 256;
19 static DEFINE_PER_CPU(struct list_head, blk_cpu_iopoll);
22 * blk_iopoll_sched - Schedule a run of the iopoll handler
23 * @iop: The parent iopoll structure
26 * Add this blk_iopoll structure to the pending poll list and trigger the
27 * raise of the blk iopoll softirq. The driver must already have gotten a
28 * successful return from blk_iopoll_sched_prep() before calling this.
30 void blk_iopoll_sched(struct blk_iopoll *iop)
34 local_irq_save(flags);
35 list_add_tail(&iop->list, this_cpu_ptr(&blk_cpu_iopoll));
36 __raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
37 local_irq_restore(flags);
38 preempt_check_resched_rt();
40 EXPORT_SYMBOL(blk_iopoll_sched);
43 * __blk_iopoll_complete - Mark this @iop as un-polled again
44 * @iop: The parent iopoll structure
47 * See blk_iopoll_complete(). This function must be called with interrupts
50 void __blk_iopoll_complete(struct blk_iopoll *iop)
53 smp_mb__before_atomic();
54 clear_bit_unlock(IOPOLL_F_SCHED, &iop->state);
56 EXPORT_SYMBOL(__blk_iopoll_complete);
59 * blk_iopoll_complete - Mark this @iop as un-polled again
60 * @iop: The parent iopoll structure
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()
68 void blk_iopoll_complete(struct blk_iopoll *iop)
72 local_irq_save(flags);
73 __blk_iopoll_complete(iop);
74 local_irq_restore(flags);
76 EXPORT_SYMBOL(blk_iopoll_complete);
78 static void blk_iopoll_softirq(struct softirq_action *h)
80 struct list_head *list = this_cpu_ptr(&blk_cpu_iopoll);
81 int rearm = 0, budget = blk_iopoll_budget;
82 unsigned long start_time = jiffies;
86 while (!list_empty(list)) {
87 struct blk_iopoll *iop;
91 * If softirq window is exhausted then punt.
93 if (budget <= 0 || time_after(jiffies, start_time)) {
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.
105 iop = list_entry(list->next, struct blk_iopoll, list);
107 weight = iop->weight;
109 if (test_bit(IOPOLL_F_SCHED, &iop->state))
110 work = iop->poll(iop, weight);
117 * Drivers must not modify the iopoll state, if they
118 * consume their assigned weight (or more, some drivers can't
119 * easily just stop processing, they have to complete an
120 * entire mask of commands).In such cases this code
121 * still "owns" the iopoll instance and therefore can
122 * move the instance around on the list at-will.
124 if (work >= weight) {
125 if (blk_iopoll_disable_pending(iop))
126 __blk_iopoll_complete(iop);
128 list_move_tail(&iop->list, list);
133 __raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
136 preempt_check_resched_rt();
140 * blk_iopoll_disable - Disable iopoll on this @iop
141 * @iop: The parent iopoll structure
144 * Disable io polling and wait for any pending callbacks to have completed.
146 void blk_iopoll_disable(struct blk_iopoll *iop)
148 set_bit(IOPOLL_F_DISABLE, &iop->state);
149 while (test_and_set_bit(IOPOLL_F_SCHED, &iop->state))
151 clear_bit(IOPOLL_F_DISABLE, &iop->state);
153 EXPORT_SYMBOL(blk_iopoll_disable);
156 * blk_iopoll_enable - Enable iopoll on this @iop
157 * @iop: The parent iopoll structure
160 * Enable iopoll on this @iop. Note that the handler run will not be
161 * scheduled, it will only mark it as active.
163 void blk_iopoll_enable(struct blk_iopoll *iop)
165 BUG_ON(!test_bit(IOPOLL_F_SCHED, &iop->state));
166 smp_mb__before_atomic();
167 clear_bit_unlock(IOPOLL_F_SCHED, &iop->state);
169 EXPORT_SYMBOL(blk_iopoll_enable);
172 * blk_iopoll_init - Initialize this @iop
173 * @iop: The parent iopoll structure
174 * @weight: The default weight (or command completion budget)
175 * @poll_fn: The handler to invoke
178 * Initialize this blk_iopoll structure. Before being actively used, the
179 * driver must call blk_iopoll_enable().
181 void blk_iopoll_init(struct blk_iopoll *iop, int weight, blk_iopoll_fn *poll_fn)
183 memset(iop, 0, sizeof(*iop));
184 INIT_LIST_HEAD(&iop->list);
185 iop->weight = weight;
187 set_bit(IOPOLL_F_SCHED, &iop->state);
189 EXPORT_SYMBOL(blk_iopoll_init);
191 static int blk_iopoll_cpu_notify(struct notifier_block *self,
192 unsigned long action, void *hcpu)
195 * If a CPU goes away, splice its entries to the current CPU
196 * and trigger a run of the softirq
198 if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
199 int cpu = (unsigned long) hcpu;
202 list_splice_init(&per_cpu(blk_cpu_iopoll, cpu),
203 this_cpu_ptr(&blk_cpu_iopoll));
204 __raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
206 preempt_check_resched_rt();
212 static struct notifier_block blk_iopoll_cpu_notifier = {
213 .notifier_call = blk_iopoll_cpu_notify,
216 static __init int blk_iopoll_setup(void)
220 for_each_possible_cpu(i)
221 INIT_LIST_HEAD(&per_cpu(blk_cpu_iopoll, i));
223 open_softirq(BLOCK_IOPOLL_SOFTIRQ, blk_iopoll_softirq);
224 register_hotcpu_notifier(&blk_iopoll_cpu_notifier);
227 subsys_initcall(blk_iopoll_setup);