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
14 static LIST_HEAD(percpu_counters);
15 static DEFINE_SPINLOCK(percpu_counters_lock);
16 #endif
17
18 #ifdef CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER
19
20 static const struct debug_obj_descr percpu_counter_debug_descr;
21
percpu_counter_fixup_free(void * addr,enum debug_obj_state state)22 static 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
36 static const struct debug_obj_descr percpu_counter_debug_descr = {
37 .name = "percpu_counter",
38 .fixup_free = percpu_counter_fixup_free,
39 };
40
debug_percpu_counter_activate(struct percpu_counter * fbc)41 static 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
debug_percpu_counter_deactivate(struct percpu_counter * fbc)47 static 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 */
debug_percpu_counter_activate(struct percpu_counter * fbc)54 static inline void debug_percpu_counter_activate(struct percpu_counter *fbc)
55 { }
debug_percpu_counter_deactivate(struct percpu_counter * fbc)56 static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc)
57 { }
58 #endif /* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */
59
percpu_counter_set(struct percpu_counter * fbc,s64 amount)60 void 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 }
73 EXPORT_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 */
percpu_counter_add_batch(struct percpu_counter * fbc,s64 amount,s32 batch)82 void 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 (abs(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 }
99 EXPORT_SYMBOL(percpu_counter_add_batch);
100
101 /*
102 * For percpu_counter with a big batch, the devication of its count could
103 * be big, and there is requirement to reduce the deviation, like when the
104 * counter's batch could be runtime decreased to get a better accuracy,
105 * which can be achieved by running this sync function on each CPU.
106 */
percpu_counter_sync(struct percpu_counter * fbc)107 void percpu_counter_sync(struct percpu_counter *fbc)
108 {
109 unsigned long flags;
110 s64 count;
111
112 raw_spin_lock_irqsave(&fbc->lock, flags);
113 count = __this_cpu_read(*fbc->counters);
114 fbc->count += count;
115 __this_cpu_sub(*fbc->counters, count);
116 raw_spin_unlock_irqrestore(&fbc->lock, flags);
117 }
118 EXPORT_SYMBOL(percpu_counter_sync);
119
120 /*
121 * Add up all the per-cpu counts, return the result. This is a more accurate
122 * but much slower version of percpu_counter_read_positive()
123 */
__percpu_counter_sum(struct percpu_counter * fbc)124 s64 __percpu_counter_sum(struct percpu_counter *fbc)
125 {
126 s64 ret;
127 int cpu;
128 unsigned long flags;
129
130 raw_spin_lock_irqsave(&fbc->lock, flags);
131 ret = fbc->count;
132 for_each_online_cpu(cpu) {
133 s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
134 ret += *pcount;
135 }
136 raw_spin_unlock_irqrestore(&fbc->lock, flags);
137 return ret;
138 }
139 EXPORT_SYMBOL(__percpu_counter_sum);
140
__percpu_counter_init(struct percpu_counter * fbc,s64 amount,gfp_t gfp,struct lock_class_key * key)141 int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, gfp_t gfp,
142 struct lock_class_key *key)
143 {
144 unsigned long flags __maybe_unused;
145
146 raw_spin_lock_init(&fbc->lock);
147 lockdep_set_class(&fbc->lock, key);
148 fbc->count = amount;
149 fbc->counters = alloc_percpu_gfp(s32, gfp);
150 if (!fbc->counters)
151 return -ENOMEM;
152
153 debug_percpu_counter_activate(fbc);
154
155 #ifdef CONFIG_HOTPLUG_CPU
156 INIT_LIST_HEAD(&fbc->list);
157 spin_lock_irqsave(&percpu_counters_lock, flags);
158 list_add(&fbc->list, &percpu_counters);
159 spin_unlock_irqrestore(&percpu_counters_lock, flags);
160 #endif
161 return 0;
162 }
163 EXPORT_SYMBOL(__percpu_counter_init);
164
percpu_counter_destroy(struct percpu_counter * fbc)165 void percpu_counter_destroy(struct percpu_counter *fbc)
166 {
167 unsigned long flags __maybe_unused;
168
169 if (!fbc->counters)
170 return;
171
172 debug_percpu_counter_deactivate(fbc);
173
174 #ifdef CONFIG_HOTPLUG_CPU
175 spin_lock_irqsave(&percpu_counters_lock, flags);
176 list_del(&fbc->list);
177 spin_unlock_irqrestore(&percpu_counters_lock, flags);
178 #endif
179 free_percpu(fbc->counters);
180 fbc->counters = NULL;
181 }
182 EXPORT_SYMBOL(percpu_counter_destroy);
183
184 int percpu_counter_batch __read_mostly = 32;
185 EXPORT_SYMBOL(percpu_counter_batch);
186
compute_batch_value(unsigned int cpu)187 static int compute_batch_value(unsigned int cpu)
188 {
189 int nr = num_online_cpus();
190
191 percpu_counter_batch = max(32, nr*2);
192 return 0;
193 }
194
percpu_counter_cpu_dead(unsigned int cpu)195 static int percpu_counter_cpu_dead(unsigned int cpu)
196 {
197 #ifdef CONFIG_HOTPLUG_CPU
198 struct percpu_counter *fbc;
199
200 compute_batch_value(cpu);
201
202 spin_lock_irq(&percpu_counters_lock);
203 list_for_each_entry(fbc, &percpu_counters, list) {
204 s32 *pcount;
205
206 raw_spin_lock(&fbc->lock);
207 pcount = per_cpu_ptr(fbc->counters, cpu);
208 fbc->count += *pcount;
209 *pcount = 0;
210 raw_spin_unlock(&fbc->lock);
211 }
212 spin_unlock_irq(&percpu_counters_lock);
213 #endif
214 return 0;
215 }
216
217 /*
218 * Compare counter against given value.
219 * Return 1 if greater, 0 if equal and -1 if less
220 */
__percpu_counter_compare(struct percpu_counter * fbc,s64 rhs,s32 batch)221 int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch)
222 {
223 s64 count;
224
225 count = percpu_counter_read(fbc);
226 /* Check to see if rough count will be sufficient for comparison */
227 if (abs(count - rhs) > (batch * num_online_cpus())) {
228 if (count > rhs)
229 return 1;
230 else
231 return -1;
232 }
233 /* Need to use precise count */
234 count = percpu_counter_sum(fbc);
235 if (count > rhs)
236 return 1;
237 else if (count < rhs)
238 return -1;
239 else
240 return 0;
241 }
242 EXPORT_SYMBOL(__percpu_counter_compare);
243
percpu_counter_startup(void)244 static int __init percpu_counter_startup(void)
245 {
246 int ret;
247
248 ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "lib/percpu_cnt:online",
249 compute_batch_value, NULL);
250 WARN_ON(ret < 0);
251 ret = cpuhp_setup_state_nocalls(CPUHP_PERCPU_CNT_DEAD,
252 "lib/percpu_cnt:dead", NULL,
253 percpu_counter_cpu_dead);
254 WARN_ON(ret < 0);
255 return 0;
256 }
257 module_init(percpu_counter_startup);
258
