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 *     successful 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