2 * Fast batching percpu counters.
5 #include <linux/percpu_counter.h>
6 #include <linux/notifier.h>
7 #include <linux/mutex.h>
8 #include <linux/init.h>
10 #include <linux/module.h>
12 static LIST_HEAD(percpu_counters);
13 static DEFINE_MUTEX(percpu_counters_lock);
15 void percpu_counter_set(struct percpu_counter *fbc, s64 amount)
19 spin_lock(&fbc->lock);
20 for_each_possible_cpu(cpu) {
21 s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
25 spin_unlock(&fbc->lock);
27 EXPORT_SYMBOL(percpu_counter_set);
29 void __percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch)
35 pcount = per_cpu_ptr(fbc->counters, cpu);
36 count = *pcount + amount;
37 if (count >= batch || count <= -batch) {
38 spin_lock(&fbc->lock);
41 spin_unlock(&fbc->lock);
47 EXPORT_SYMBOL(__percpu_counter_add);
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()
53 s64 __percpu_counter_sum(struct percpu_counter *fbc)
58 spin_lock(&fbc->lock);
60 for_each_online_cpu(cpu) {
61 s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
64 spin_unlock(&fbc->lock);
67 EXPORT_SYMBOL(__percpu_counter_sum);
69 static struct lock_class_key percpu_counter_irqsafe;
71 int percpu_counter_init(struct percpu_counter *fbc, s64 amount)
73 spin_lock_init(&fbc->lock);
75 fbc->counters = alloc_percpu(s32);
78 #ifdef CONFIG_HOTPLUG_CPU
79 mutex_lock(&percpu_counters_lock);
80 list_add(&fbc->list, &percpu_counters);
81 mutex_unlock(&percpu_counters_lock);
85 EXPORT_SYMBOL(percpu_counter_init);
87 int percpu_counter_init_irq(struct percpu_counter *fbc, s64 amount)
91 err = percpu_counter_init(fbc, amount);
93 lockdep_set_class(&fbc->lock, &percpu_counter_irqsafe);
97 void percpu_counter_destroy(struct percpu_counter *fbc)
102 #ifdef CONFIG_HOTPLUG_CPU
103 mutex_lock(&percpu_counters_lock);
104 list_del(&fbc->list);
105 mutex_unlock(&percpu_counters_lock);
107 free_percpu(fbc->counters);
108 fbc->counters = NULL;
110 EXPORT_SYMBOL(percpu_counter_destroy);
112 int percpu_counter_batch __read_mostly = 32;
113 EXPORT_SYMBOL(percpu_counter_batch);
115 static void compute_batch_value(void)
117 int nr = num_online_cpus();
119 percpu_counter_batch = max(32, nr*2);
122 static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
123 unsigned long action, void *hcpu)
125 #ifdef CONFIG_HOTPLUG_CPU
127 struct percpu_counter *fbc;
129 compute_batch_value();
130 if (action != CPU_DEAD)
133 cpu = (unsigned long)hcpu;
134 mutex_lock(&percpu_counters_lock);
135 list_for_each_entry(fbc, &percpu_counters, list) {
139 spin_lock_irqsave(&fbc->lock, flags);
140 pcount = per_cpu_ptr(fbc->counters, cpu);
141 fbc->count += *pcount;
143 spin_unlock_irqrestore(&fbc->lock, flags);
145 mutex_unlock(&percpu_counters_lock);
150 static int __init percpu_counter_startup(void)
152 compute_batch_value();
153 hotcpu_notifier(percpu_counter_hotcpu_callback, 0);
156 module_init(percpu_counter_startup);