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
12 static LIST_HEAD(percpu_counters);
13 static DEFINE_MUTEX(percpu_counters_lock);
14
15 void percpu_counter_set(struct percpu_counter *fbc, s64 amount)
16 {
17 int cpu;
18
19 spin_lock(&fbc->lock);
20 for_each_possible_cpu(cpu) {
21 s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
22 *pcount = 0;
23 }
24 fbc->count = amount;
25 spin_unlock(&fbc->lock);
26 }
27 EXPORT_SYMBOL(percpu_counter_set);
28
29 void __percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch)
30 {
31 s64 count;
32 s32 *pcount;
33 int cpu = get_cpu();
34
35 pcount = per_cpu_ptr(fbc->counters, cpu);
36 count = *pcount + amount;
37 if (count >= batch || count <= -batch) {
38 spin_lock(&fbc->lock);
39 fbc->count += count;
40 *pcount = 0;
41 spin_unlock(&fbc->lock);
42 } else {
43 *pcount = count;
44 }
45 put_cpu();
46 }
47 EXPORT_SYMBOL(__percpu_counter_add);
48
49 /*
50 * Add up all the per-cpu counts, return the result. This is a more accurate
51 * but much slower version of percpu_counter_read_positive()
52 */
53 s64 __percpu_counter_sum(struct percpu_counter *fbc)
54 {
55 s64 ret;
56 int cpu;
57
58 spin_lock(&fbc->lock);
59 ret = fbc->count;
60 for_each_online_cpu(cpu) {
61 s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
62 ret += *pcount;
63 }
64 spin_unlock(&fbc->lock);
65 return ret;
66 }
67 EXPORT_SYMBOL(__percpu_counter_sum);
68
69 int __percpu_counter_init(struct percpu_counter *fbc, s64 amount,
70 struct lock_class_key *key)
71 {
72 spin_lock_init(&fbc->lock);
73 lockdep_set_class(&fbc->lock, key);
74 fbc->count = amount;
75 fbc->counters = alloc_percpu(s32);
76 if (!fbc->counters)
77 return -ENOMEM;
78 #ifdef CONFIG_HOTPLUG_CPU
79 mutex_lock(&percpu_counters_lock);
80 list_add(&fbc->list, &percpu_counters);
81 mutex_unlock(&percpu_counters_lock);
82 #endif
83 return 0;
84 }
85 EXPORT_SYMBOL(__percpu_counter_init);
86
87 void percpu_counter_destroy(struct percpu_counter *fbc)
88 {
89 if (!fbc->counters)
90 return;
91
92 #ifdef CONFIG_HOTPLUG_CPU
93 mutex_lock(&percpu_counters_lock);
94 list_del(&fbc->list);
95 mutex_unlock(&percpu_counters_lock);
96 #endif
97 free_percpu(fbc->counters);
98 fbc->counters = NULL;
99 }
100 EXPORT_SYMBOL(percpu_counter_destroy);
101
102 int percpu_counter_batch __read_mostly = 32;
103 EXPORT_SYMBOL(percpu_counter_batch);
104
105 static void compute_batch_value(void)
106 {
107 int nr = num_online_cpus();
108
109 percpu_counter_batch = max(32, nr*2);
110 }
111
112 static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
113 unsigned long action, void *hcpu)
114 {
115 #ifdef CONFIG_HOTPLUG_CPU
116 unsigned int cpu;
117 struct percpu_counter *fbc;
118
119 compute_batch_value();
120 if (action != CPU_DEAD)
121 return NOTIFY_OK;
122
123 cpu = (unsigned long)hcpu;
124 mutex_lock(&percpu_counters_lock);
125 list_for_each_entry(fbc, &percpu_counters, list) {
126 s32 *pcount;
127 unsigned long flags;
128
129 spin_lock_irqsave(&fbc->lock, flags);
130 pcount = per_cpu_ptr(fbc->counters, cpu);
131 fbc->count += *pcount;
132 *pcount = 0;
133 spin_unlock_irqrestore(&fbc->lock, flags);
134 }
135 mutex_unlock(&percpu_counters_lock);
136 #endif
137 return NOTIFY_OK;
138 }
139
140 static int __init percpu_counter_startup(void)
141 {
142 compute_batch_value();
143 hotcpu_notifier(percpu_counter_hotcpu_callback, 0);
144 return 0;
145 }
146 module_init(percpu_counter_startup);
147
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