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path: root/lib/percpu_counter.c (plain)
blob: 72d36113ccaa8509a7140b506cdc0330690a8b15
1/*
2 * Fast batching percpu counters.
3 */
4
5#include <linux/percpu_counter.h>
6#include <linux/notifier.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
75void __percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch)
76{
77 s64 count;
78
79 preempt_disable();
80 count = __this_cpu_read(*fbc->counters) + amount;
81 if (count >= batch || count <= -batch) {
82 unsigned long flags;
83 raw_spin_lock_irqsave(&fbc->lock, flags);
84 fbc->count += count;
85 __this_cpu_sub(*fbc->counters, count - amount);
86 raw_spin_unlock_irqrestore(&fbc->lock, flags);
87 } else {
88 this_cpu_add(*fbc->counters, amount);
89 }
90 preempt_enable();
91}
92EXPORT_SYMBOL(__percpu_counter_add);
93
94/*
95 * Add up all the per-cpu counts, return the result. This is a more accurate
96 * but much slower version of percpu_counter_read_positive()
97 */
98s64 __percpu_counter_sum(struct percpu_counter *fbc)
99{
100 s64 ret;
101 int cpu;
102 unsigned long flags;
103
104 raw_spin_lock_irqsave(&fbc->lock, flags);
105 ret = fbc->count;
106 for_each_online_cpu(cpu) {
107 s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
108 ret += *pcount;
109 }
110 raw_spin_unlock_irqrestore(&fbc->lock, flags);
111 return ret;
112}
113EXPORT_SYMBOL(__percpu_counter_sum);
114
115int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, gfp_t gfp,
116 struct lock_class_key *key)
117{
118 unsigned long flags __maybe_unused;
119
120 raw_spin_lock_init(&fbc->lock);
121 lockdep_set_class(&fbc->lock, key);
122 fbc->count = amount;
123 fbc->counters = alloc_percpu_gfp(s32, gfp);
124 if (!fbc->counters)
125 return -ENOMEM;
126
127 debug_percpu_counter_activate(fbc);
128
129#ifdef CONFIG_HOTPLUG_CPU
130 INIT_LIST_HEAD(&fbc->list);
131 spin_lock_irqsave(&percpu_counters_lock, flags);
132 list_add(&fbc->list, &percpu_counters);
133 spin_unlock_irqrestore(&percpu_counters_lock, flags);
134#endif
135 return 0;
136}
137EXPORT_SYMBOL(__percpu_counter_init);
138
139void percpu_counter_destroy(struct percpu_counter *fbc)
140{
141 unsigned long flags __maybe_unused;
142
143 if (!fbc->counters)
144 return;
145
146 debug_percpu_counter_deactivate(fbc);
147
148#ifdef CONFIG_HOTPLUG_CPU
149 spin_lock_irqsave(&percpu_counters_lock, flags);
150 list_del(&fbc->list);
151 spin_unlock_irqrestore(&percpu_counters_lock, flags);
152#endif
153 free_percpu(fbc->counters);
154 fbc->counters = NULL;
155}
156EXPORT_SYMBOL(percpu_counter_destroy);
157
158int percpu_counter_batch __read_mostly = 32;
159EXPORT_SYMBOL(percpu_counter_batch);
160
161static void compute_batch_value(void)
162{
163 int nr = num_online_cpus();
164
165 percpu_counter_batch = max(32, nr*2);
166}
167
168static int percpu_counter_hotcpu_callback(struct notifier_block *nb,
169 unsigned long action, void *hcpu)
170{
171#ifdef CONFIG_HOTPLUG_CPU
172 unsigned int cpu;
173 struct percpu_counter *fbc;
174
175 compute_batch_value();
176 if (action != CPU_DEAD && action != CPU_DEAD_FROZEN)
177 return NOTIFY_OK;
178
179 cpu = (unsigned long)hcpu;
180 spin_lock_irq(&percpu_counters_lock);
181 list_for_each_entry(fbc, &percpu_counters, list) {
182 s32 *pcount;
183 unsigned long flags;
184
185 raw_spin_lock_irqsave(&fbc->lock, flags);
186 pcount = per_cpu_ptr(fbc->counters, cpu);
187 fbc->count += *pcount;
188 *pcount = 0;
189 raw_spin_unlock_irqrestore(&fbc->lock, flags);
190 }
191 spin_unlock_irq(&percpu_counters_lock);
192#endif
193 return NOTIFY_OK;
194}
195
196/*
197 * Compare counter against given value.
198 * Return 1 if greater, 0 if equal and -1 if less
199 */
200int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch)
201{
202 s64 count;
203
204 count = percpu_counter_read(fbc);
205 /* Check to see if rough count will be sufficient for comparison */
206 if (abs(count - rhs) > (batch * num_online_cpus())) {
207 if (count > rhs)
208 return 1;
209 else
210 return -1;
211 }
212 /* Need to use precise count */
213 count = percpu_counter_sum(fbc);
214 if (count > rhs)
215 return 1;
216 else if (count < rhs)
217 return -1;
218 else
219 return 0;
220}
221EXPORT_SYMBOL(__percpu_counter_compare);
222
223static int __init percpu_counter_startup(void)
224{
225 compute_batch_value();
226 hotcpu_notifier(percpu_counter_hotcpu_callback, 0);
227 return 0;
228}
229module_init(percpu_counter_startup);
230
generated by cgit at 2024-05-18 14:37:46 (GMT)