1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Functions related to interrupt-poll handling in the block layer. This
4 * is similar to NAPI for network devices.
5 */
6 #include <linux/kernel.h>
7 #include <linux/module.h>
8 #include <linux/init.h>
9 #include <linux/bio.h>
10 #include <linux/interrupt.h>
11 #include <linux/cpu.h>
12 #include <linux/irq_poll.h>
13 #include <linux/delay.h>
14
15 static unsigned int irq_poll_budget __read_mostly = 256;
16
17 static DEFINE_PER_CPU(struct list_head, blk_cpu_iopoll);
18
19 /**
20 * irq_poll_sched - Schedule a run of the iopoll handler
21 * @iop: The parent iopoll structure
22 *
23 * Description:
24 * Add this irq_poll structure to the pending poll list and trigger the
25 * raise of the blk iopoll softirq.
26 **/
27 void irq_poll_sched(struct irq_poll *iop)
28 {
29 unsigned long flags;
30
31 if (test_bit(IRQ_POLL_F_DISABLE, &iop->state))
32 return;
33 if (test_and_set_bit(IRQ_POLL_F_SCHED, &iop->state))
34 return;
35
36 local_irq_save(flags);
37 list_add_tail(&iop->list, this_cpu_ptr(&blk_cpu_iopoll));
38 raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
39 local_irq_restore(flags);
40 }
41 EXPORT_SYMBOL(irq_poll_sched);
42
43 /**
44 * __irq_poll_complete - Mark this @iop as un-polled again
45 * @iop: The parent iopoll structure
46 *
47 * Description:
48 * See irq_poll_complete(). This function must be called with interrupts
49 * disabled.
50 **/
51 static void __irq_poll_complete(struct irq_poll *iop)
52 {
53 list_del(&iop->list);
54 smp_mb__before_atomic();
55 clear_bit_unlock(IRQ_POLL_F_SCHED, &iop->state);
56 }
57
58 /**
59 * irq_poll_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 irq_poll_sched()
66 * is called.
67 **/
68 void irq_poll_complete(struct irq_poll *iop)
69 {
70 unsigned long flags;
71
72 local_irq_save(flags);
73 __irq_poll_complete(iop);
74 local_irq_restore(flags);
75 }
76 EXPORT_SYMBOL(irq_poll_complete);
77
78 static void __latent_entropy irq_poll_softirq(struct softirq_action *h)
79 {
80 struct list_head *list = this_cpu_ptr(&blk_cpu_iopoll);
81 int rearm = 0, budget = irq_poll_budget;
82 unsigned long start_time = jiffies;
83
84 local_irq_disable();
85
86 while (!list_empty(list)) {
87 struct irq_poll *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 irq_poll, list);
106
107 weight = iop->weight;
108 work = 0;
109 if (test_bit(IRQ_POLL_F_SCHED, &iop->state))
110 work = iop->poll(iop, weight);
111
112 budget -= work;
113
114 local_irq_disable();
115
116 /*
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.
123 */
124 if (work >= weight) {
125 if (test_bit(IRQ_POLL_F_DISABLE, &iop->state))
126 __irq_poll_complete(iop);
127 else
128 list_move_tail(&iop->list, list);
129 }
130 }
131
132 if (rearm)
133 __raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
134
135 local_irq_enable();
136 }
137
138 /**
139 * irq_poll_disable - Disable iopoll on this @iop
140 * @iop: The parent iopoll structure
141 *
142 * Description:
143 * Disable io polling and wait for any pending callbacks to have completed.
144 **/
145 void irq_poll_disable(struct irq_poll *iop)
146 {
147 set_bit(IRQ_POLL_F_DISABLE, &iop->state);
148 while (test_and_set_bit(IRQ_POLL_F_SCHED, &iop->state))
149 msleep(1);
150 clear_bit(IRQ_POLL_F_DISABLE, &iop->state);
151 }
152 EXPORT_SYMBOL(irq_poll_disable);
153
154 /**
155 * irq_poll_enable - Enable iopoll on this @iop
156 * @iop: The parent iopoll structure
157 *
158 * Description:
159 * Enable iopoll on this @iop. Note that the handler run will not be
160 * scheduled, it will only mark it as active.
161 **/
162 void irq_poll_enable(struct irq_poll *iop)
163 {
164 BUG_ON(!test_bit(IRQ_POLL_F_SCHED, &iop->state));
165 smp_mb__before_atomic();
166 clear_bit_unlock(IRQ_POLL_F_SCHED, &iop->state);
167 }
168 EXPORT_SYMBOL(irq_poll_enable);
169
170 /**
171 * irq_poll_init - Initialize this @iop
172 * @iop: The parent iopoll structure
173 * @weight: The default weight (or command completion budget)
174 * @poll_fn: The handler to invoke
175 *
176 * Description:
177 * Initialize and enable this irq_poll structure.
178 **/
179 void irq_poll_init(struct irq_poll *iop, int weight, irq_poll_fn *poll_fn)
180 {
181 memset(iop, 0, sizeof(*iop));
182 INIT_LIST_HEAD(&iop->list);
183 iop->weight = weight;
184 iop->poll = poll_fn;
185 }
186 EXPORT_SYMBOL(irq_poll_init);
187
188 static int irq_poll_cpu_dead(unsigned int cpu)
189 {
190 /*
191 * If a CPU goes away, splice its entries to the current CPU and
192 * set the POLL softirq bit. The local_bh_disable()/enable() pair
193 * ensures that it is handled. Otherwise the current CPU could
194 * reach idle with the POLL softirq pending.
195 */
196 local_bh_disable();
197 local_irq_disable();
198 list_splice_init(&per_cpu(blk_cpu_iopoll, cpu),
199 this_cpu_ptr(&blk_cpu_iopoll));
200 __raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
201 local_irq_enable();
202 local_bh_enable();
203
204 return 0;
205 }
206
207 static __init int irq_poll_setup(void)
208 {
209 int i;
210
211 for_each_possible_cpu(i)
212 INIT_LIST_HEAD(&per_cpu(blk_cpu_iopoll, i));
213
214 open_softirq(IRQ_POLL_SOFTIRQ, irq_poll_softirq);
215 cpuhp_setup_state_nocalls(CPUHP_IRQ_POLL_DEAD, "irq_poll:dead", NULL,
216 irq_poll_cpu_dead);
217 return 0;
218 }
219 subsys_initcall(irq_poll_setup);
220
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