1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Fast batching percpu counters.
4 */
5
6#include <linux/percpu_counter.h>
7#include <linux/mutex.h>
8#include <linux/init.h>
9#include <linux/cpu.h>
10#include <linux/module.h>
11#include <linux/debugobjects.h>
12
13#ifdef CONFIG_HOTPLUG_CPU
14static LIST_HEAD(percpu_counters);
15static DEFINE_SPINLOCK(percpu_counters_lock);
16#endif
17
18#ifdef CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER
19
20static struct debug_obj_descr percpu_counter_debug_descr;
21
22static bool percpu_counter_fixup_free(void *addr, enum debug_obj_state state)
23{
24 struct percpu_counter *fbc = addr;
25
26 switch (state) {
27 case ODEBUG_STATE_ACTIVE:
28 percpu_counter_destroy(fbc);
29 debug_object_free(fbc, &percpu_counter_debug_descr);
30 return true;
31 default:
32 return false;
33 }
34}
35
36static struct debug_obj_descr percpu_counter_debug_descr = {
37 .name = "percpu_counter",
38 .fixup_free = percpu_counter_fixup_free,
39};
40
41static inline void debug_percpu_counter_activate(struct percpu_counter *fbc)
42{
43 debug_object_init(fbc, &percpu_counter_debug_descr);
44 debug_object_activate(fbc, &percpu_counter_debug_descr);
45}
46
47static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc)
48{
49 debug_object_deactivate(fbc, &percpu_counter_debug_descr);
50 debug_object_free(fbc, &percpu_counter_debug_descr);
51}
52
53#else /* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */
54static inline void debug_percpu_counter_activate(struct percpu_counter *fbc)
55{ }
56static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc)
57{ }
58#endif /* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */
59
60void percpu_counter_set(struct percpu_counter *fbc, s64 amount)
61{
62 int cpu;
63 unsigned long flags;
64
65 raw_spin_lock_irqsave(&fbc->lock, flags);
66 for_each_possible_cpu(cpu) {
67 s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
68 *pcount = 0;
69 }
70 fbc->count = amount;
71 raw_spin_unlock_irqrestore(&fbc->lock, flags);
72}
73EXPORT_SYMBOL(percpu_counter_set);
74
75/**
76 * This function is both preempt and irq safe. The former is due to explicit
77 * preemption disable. The latter is guaranteed by the fact that the slow path
78 * is explicitly protected by an irq-safe spinlock whereas the fast patch uses
79 * this_cpu_add which is irq-safe by definition. Hence there is no need muck
80 * with irq state before calling this one
81 */
82void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch)
83{
84 s64 count;
85
86 preempt_disable();
87 count = __this_cpu_read(*fbc->counters) + amount;
88 if (count >= batch || count <= -batch) {
89 unsigned long flags;
90 raw_spin_lock_irqsave(&fbc->lock, flags);
91 fbc->count += count;
92 __this_cpu_sub(*fbc->counters, count - amount);
93 raw_spin_unlock_irqrestore(&fbc->lock, flags);
94 } else {
95 this_cpu_add(*fbc->counters, amount);
96 }
97 preempt_enable();
98}
99EXPORT_SYMBOL(percpu_counter_add_batch);
100
101/*
102 * Add up all the per-cpu counts, return the result. This is a more accurate
103 * but much slower version of percpu_counter_read_positive()
104 */
105s64 __percpu_counter_sum(struct percpu_counter *fbc)
106{
107 s64 ret;
108 int cpu;
109 unsigned long flags;
110
111 raw_spin_lock_irqsave(&fbc->lock, flags);
112 ret = fbc->count;
113 for_each_online_cpu(cpu) {
114 s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
115 ret += *pcount;
116 }
117 raw_spin_unlock_irqrestore(&fbc->lock, flags);
118 return ret;
119}
120EXPORT_SYMBOL(__percpu_counter_sum);
121
122int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, gfp_t gfp,
123 struct lock_class_key *key)
124{
125 unsigned long flags __maybe_unused;
126
127 raw_spin_lock_init(&fbc->lock);
128 lockdep_set_class(&fbc->lock, key);
129 fbc->count = amount;
130 fbc->counters = alloc_percpu_gfp(s32, gfp);
131 if (!fbc->counters)
132 return -ENOMEM;
133
134 debug_percpu_counter_activate(fbc);
135
136#ifdef CONFIG_HOTPLUG_CPU
137 INIT_LIST_HEAD(&fbc->list);
138 spin_lock_irqsave(&percpu_counters_lock, flags);
139 list_add(&fbc->list, &percpu_counters);
140 spin_unlock_irqrestore(&percpu_counters_lock, flags);
141#endif
142 return 0;
143}
144EXPORT_SYMBOL(__percpu_counter_init);
145
146void percpu_counter_destroy(struct percpu_counter *fbc)
147{
148 unsigned long flags __maybe_unused;
149
150 if (!fbc->counters)
151 return;
152
153 debug_percpu_counter_deactivate(fbc);
154
155#ifdef CONFIG_HOTPLUG_CPU
156 spin_lock_irqsave(&percpu_counters_lock, flags);
157 list_del(&fbc->list);
158 spin_unlock_irqrestore(&percpu_counters_lock, flags);
159#endif
160 free_percpu(fbc->counters);
161 fbc->counters = NULL;
162}
163EXPORT_SYMBOL(percpu_counter_destroy);
164
165int percpu_counter_batch __read_mostly = 32;
166EXPORT_SYMBOL(percpu_counter_batch);
167
168static int compute_batch_value(unsigned int cpu)
169{
170 int nr = num_online_cpus();
171
172 percpu_counter_batch = max(32, nr*2);
173 return 0;
174}
175
176static int percpu_counter_cpu_dead(unsigned int cpu)
177{
178#ifdef CONFIG_HOTPLUG_CPU
179 struct percpu_counter *fbc;
180
181 compute_batch_value(cpu);
182
183 spin_lock_irq(&percpu_counters_lock);
184 list_for_each_entry(fbc, &percpu_counters, list) {
185 s32 *pcount;
186
187 raw_spin_lock(&fbc->lock);
188 pcount = per_cpu_ptr(fbc->counters, cpu);
189 fbc->count += *pcount;
190 *pcount = 0;
191 raw_spin_unlock(&fbc->lock);
192 }
193 spin_unlock_irq(&percpu_counters_lock);
194#endif
195 return 0;
196}
197
198/*
199 * Compare counter against given value.
200 * Return 1 if greater, 0 if equal and -1 if less
201 */
202int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch)
203{
204 s64 count;
205
206 count = percpu_counter_read(fbc);
207 /* Check to see if rough count will be sufficient for comparison */
208 if (abs(count - rhs) > (batch * num_online_cpus())) {
209 if (count > rhs)
210 return 1;
211 else
212 return -1;
213 }
214 /* Need to use precise count */
215 count = percpu_counter_sum(fbc);
216 if (count > rhs)
217 return 1;
218 else if (count < rhs)
219 return -1;
220 else
221 return 0;
222}
223EXPORT_SYMBOL(__percpu_counter_compare);
224
225static int __init percpu_counter_startup(void)
226{
227 int ret;
228
229 ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "lib/percpu_cnt:online",
230 compute_batch_value, NULL);
231 WARN_ON(ret < 0);
232 ret = cpuhp_setup_state_nocalls(CPUHP_PERCPU_CNT_DEAD,
233 "lib/percpu_cnt:dead", NULL,
234 percpu_counter_cpu_dead);
235 WARN_ON(ret < 0);
236 return 0;
237}
238module_init(percpu_counter_startup);
239