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 const 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(addr: fbc, descr: &percpu_counter_debug_descr);
30 return true;
31 default:
32 return false;
33 }
34}
35
36static const 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(addr: fbc, descr: &percpu_counter_debug_descr);
44 debug_object_activate(addr: fbc, descr: &percpu_counter_debug_descr);
45}
46
47static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc)
48{
49 debug_object_deactivate(addr: fbc, descr: &percpu_counter_debug_descr);
50 debug_object_free(addr: fbc, descr: &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 * local_irq_save() is needed to make the function irq safe:
77 * - The slow path would be ok as protected by an irq-safe spinlock.
78 * - this_cpu_add would be ok as it is irq-safe by definition.
79 * But:
80 * The decision slow path/fast path and the actual update must be atomic, too.
81 * Otherwise a call in process context could check the current values and
82 * decide that the fast path can be used. If now an interrupt occurs before
83 * the this_cpu_add(), and the interrupt updates this_cpu(*fbc->counters),
84 * then the this_cpu_add() that is executed after the interrupt has completed
85 * can produce values larger than "batch" or even overflows.
86 */
87void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch)
88{
89 s64 count;
90 unsigned long flags;
91
92 local_irq_save(flags);
93 count = __this_cpu_read(*fbc->counters) + amount;
94 if (abs(count) >= batch) {
95 raw_spin_lock(&fbc->lock);
96 fbc->count += count;
97 __this_cpu_sub(*fbc->counters, count - amount);
98 raw_spin_unlock(&fbc->lock);
99 } else {
100 this_cpu_add(*fbc->counters, amount);
101 }
102 local_irq_restore(flags);
103}
104EXPORT_SYMBOL(percpu_counter_add_batch);
105
106/*
107 * For percpu_counter with a big batch, the devication of its count could
108 * be big, and there is requirement to reduce the deviation, like when the
109 * counter's batch could be runtime decreased to get a better accuracy,
110 * which can be achieved by running this sync function on each CPU.
111 */
112void percpu_counter_sync(struct percpu_counter *fbc)
113{
114 unsigned long flags;
115 s64 count;
116
117 raw_spin_lock_irqsave(&fbc->lock, flags);
118 count = __this_cpu_read(*fbc->counters);
119 fbc->count += count;
120 __this_cpu_sub(*fbc->counters, count);
121 raw_spin_unlock_irqrestore(&fbc->lock, flags);
122}
123EXPORT_SYMBOL(percpu_counter_sync);
124
125/*
126 * Add up all the per-cpu counts, return the result. This is a more accurate
127 * but much slower version of percpu_counter_read_positive().
128 *
129 * We use the cpu mask of (cpu_online_mask | cpu_dying_mask) to capture sums
130 * from CPUs that are in the process of being taken offline. Dying cpus have
131 * been removed from the online mask, but may not have had the hotplug dead
132 * notifier called to fold the percpu count back into the global counter sum.
133 * By including dying CPUs in the iteration mask, we avoid this race condition
134 * so __percpu_counter_sum() just does the right thing when CPUs are being taken
135 * offline.
136 */
137s64 __percpu_counter_sum(struct percpu_counter *fbc)
138{
139 s64 ret;
140 int cpu;
141 unsigned long flags;
142
143 raw_spin_lock_irqsave(&fbc->lock, flags);
144 ret = fbc->count;
145 for_each_cpu_or(cpu, cpu_online_mask, cpu_dying_mask) {
146 s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
147 ret += *pcount;
148 }
149 raw_spin_unlock_irqrestore(&fbc->lock, flags);
150 return ret;
151}
152EXPORT_SYMBOL(__percpu_counter_sum);
153
154int __percpu_counter_init_many(struct percpu_counter *fbc, s64 amount,
155 gfp_t gfp, u32 nr_counters,
156 struct lock_class_key *key)
157{
158 unsigned long flags __maybe_unused;
159 size_t counter_size;
160 s32 __percpu *counters;
161 u32 i;
162
163 counter_size = ALIGN(sizeof(*counters), __alignof__(*counters));
164 counters = __alloc_percpu_gfp(size: nr_counters * counter_size,
165 align: __alignof__(*counters), gfp);
166 if (!counters) {
167 fbc[0].counters = NULL;
168 return -ENOMEM;
169 }
170
171 for (i = 0; i < nr_counters; i++) {
172 raw_spin_lock_init(&fbc[i].lock);
173 lockdep_set_class(&fbc[i].lock, key);
174#ifdef CONFIG_HOTPLUG_CPU
175 INIT_LIST_HEAD(list: &fbc[i].list);
176#endif
177 fbc[i].count = amount;
178 fbc[i].counters = (void *)counters + (i * counter_size);
179
180 debug_percpu_counter_activate(fbc: &fbc[i]);
181 }
182
183#ifdef CONFIG_HOTPLUG_CPU
184 spin_lock_irqsave(&percpu_counters_lock, flags);
185 for (i = 0; i < nr_counters; i++)
186 list_add(new: &fbc[i].list, head: &percpu_counters);
187 spin_unlock_irqrestore(lock: &percpu_counters_lock, flags);
188#endif
189 return 0;
190}
191EXPORT_SYMBOL(__percpu_counter_init_many);
192
193void percpu_counter_destroy_many(struct percpu_counter *fbc, u32 nr_counters)
194{
195 unsigned long flags __maybe_unused;
196 u32 i;
197
198 if (WARN_ON_ONCE(!fbc))
199 return;
200
201 if (!fbc[0].counters)
202 return;
203
204 for (i = 0; i < nr_counters; i++)
205 debug_percpu_counter_deactivate(fbc: &fbc[i]);
206
207#ifdef CONFIG_HOTPLUG_CPU
208 spin_lock_irqsave(&percpu_counters_lock, flags);
209 for (i = 0; i < nr_counters; i++)
210 list_del(entry: &fbc[i].list);
211 spin_unlock_irqrestore(lock: &percpu_counters_lock, flags);
212#endif
213
214 free_percpu(pdata: fbc[0].counters);
215
216 for (i = 0; i < nr_counters; i++)
217 fbc[i].counters = NULL;
218}
219EXPORT_SYMBOL(percpu_counter_destroy_many);
220
221int percpu_counter_batch __read_mostly = 32;
222EXPORT_SYMBOL(percpu_counter_batch);
223
224static int compute_batch_value(unsigned int cpu)
225{
226 int nr = num_online_cpus();
227
228 percpu_counter_batch = max(32, nr*2);
229 return 0;
230}
231
232static int percpu_counter_cpu_dead(unsigned int cpu)
233{
234#ifdef CONFIG_HOTPLUG_CPU
235 struct percpu_counter *fbc;
236
237 compute_batch_value(cpu);
238
239 spin_lock_irq(lock: &percpu_counters_lock);
240 list_for_each_entry(fbc, &percpu_counters, list) {
241 s32 *pcount;
242
243 raw_spin_lock(&fbc->lock);
244 pcount = per_cpu_ptr(fbc->counters, cpu);
245 fbc->count += *pcount;
246 *pcount = 0;
247 raw_spin_unlock(&fbc->lock);
248 }
249 spin_unlock_irq(lock: &percpu_counters_lock);
250#endif
251 return 0;
252}
253
254/*
255 * Compare counter against given value.
256 * Return 1 if greater, 0 if equal and -1 if less
257 */
258int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch)
259{
260 s64 count;
261
262 count = percpu_counter_read(fbc);
263 /* Check to see if rough count will be sufficient for comparison */
264 if (abs(count - rhs) > (batch * num_online_cpus())) {
265 if (count > rhs)
266 return 1;
267 else
268 return -1;
269 }
270 /* Need to use precise count */
271 count = percpu_counter_sum(fbc);
272 if (count > rhs)
273 return 1;
274 else if (count < rhs)
275 return -1;
276 else
277 return 0;
278}
279EXPORT_SYMBOL(__percpu_counter_compare);
280
281/*
282 * Compare counter, and add amount if total is: less than or equal to limit if
283 * amount is positive, or greater than or equal to limit if amount is negative.
284 * Return true if amount is added, or false if total would be beyond the limit.
285 *
286 * Negative limit is allowed, but unusual.
287 * When negative amounts (subs) are given to percpu_counter_limited_add(),
288 * the limit would most naturally be 0 - but other limits are also allowed.
289 *
290 * Overflow beyond S64_MAX is not allowed for: counter, limit and amount
291 * are all assumed to be sane (far from S64_MIN and S64_MAX).
292 */
293bool __percpu_counter_limited_add(struct percpu_counter *fbc,
294 s64 limit, s64 amount, s32 batch)
295{
296 s64 count;
297 s64 unknown;
298 unsigned long flags;
299 bool good = false;
300
301 if (amount == 0)
302 return true;
303
304 local_irq_save(flags);
305 unknown = batch * num_online_cpus();
306 count = __this_cpu_read(*fbc->counters);
307
308 /* Skip taking the lock when safe */
309 if (abs(count + amount) <= batch &&
310 ((amount > 0 && fbc->count + unknown <= limit) ||
311 (amount < 0 && fbc->count - unknown >= limit))) {
312 this_cpu_add(*fbc->counters, amount);
313 local_irq_restore(flags);
314 return true;
315 }
316
317 raw_spin_lock(&fbc->lock);
318 count = fbc->count + amount;
319
320 /* Skip percpu_counter_sum() when safe */
321 if (amount > 0) {
322 if (count - unknown > limit)
323 goto out;
324 if (count + unknown <= limit)
325 good = true;
326 } else {
327 if (count + unknown < limit)
328 goto out;
329 if (count - unknown >= limit)
330 good = true;
331 }
332
333 if (!good) {
334 s32 *pcount;
335 int cpu;
336
337 for_each_cpu_or(cpu, cpu_online_mask, cpu_dying_mask) {
338 pcount = per_cpu_ptr(fbc->counters, cpu);
339 count += *pcount;
340 }
341 if (amount > 0) {
342 if (count > limit)
343 goto out;
344 } else {
345 if (count < limit)
346 goto out;
347 }
348 good = true;
349 }
350
351 count = __this_cpu_read(*fbc->counters);
352 fbc->count += count + amount;
353 __this_cpu_sub(*fbc->counters, count);
354out:
355 raw_spin_unlock(&fbc->lock);
356 local_irq_restore(flags);
357 return good;
358}
359
360static int __init percpu_counter_startup(void)
361{
362 int ret;
363
364 ret = cpuhp_setup_state(state: CPUHP_AP_ONLINE_DYN, name: "lib/percpu_cnt:online",
365 startup: compute_batch_value, NULL);
366 WARN_ON(ret < 0);
367 ret = cpuhp_setup_state_nocalls(state: CPUHP_PERCPU_CNT_DEAD,
368 name: "lib/percpu_cnt:dead", NULL,
369 teardown: percpu_counter_cpu_dead);
370 WARN_ON(ret < 0);
371 return 0;
372}
373module_init(percpu_counter_startup);
374

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source code of linux/lib/percpu_counter.c