lib: percpu_counter_sum_positive
[linux-2.6.git] / lib / percpu_counter.c
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 #ifdef CONFIG_HOTPLUG_CPU
13 static LIST_HEAD(percpu_counters);
14 static DEFINE_MUTEX(percpu_counters_lock);
15 #endif
16
17 void percpu_counter_set(struct percpu_counter *fbc, s64 amount)
18 {
19         int cpu;
20
21         spin_lock(&fbc->lock);
22         for_each_possible_cpu(cpu) {
23                 s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
24                 *pcount = 0;
25         }
26         fbc->count = amount;
27         spin_unlock(&fbc->lock);
28 }
29 EXPORT_SYMBOL(percpu_counter_set);
30
31 void __percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch)
32 {
33         s64 count;
34         s32 *pcount;
35         int cpu = get_cpu();
36
37         pcount = per_cpu_ptr(fbc->counters, cpu);
38         count = *pcount + amount;
39         if (count >= batch || count <= -batch) {
40                 spin_lock(&fbc->lock);
41                 fbc->count += count;
42                 *pcount = 0;
43                 spin_unlock(&fbc->lock);
44         } else {
45                 *pcount = count;
46         }
47         put_cpu();
48 }
49 EXPORT_SYMBOL(__percpu_counter_add);
50
51 /*
52  * Add up all the per-cpu counts, return the result.  This is a more accurate
53  * but much slower version of percpu_counter_read_positive()
54  */
55 s64 percpu_counter_sum_positive(struct percpu_counter *fbc)
56 {
57         s64 ret;
58         int cpu;
59
60         spin_lock(&fbc->lock);
61         ret = fbc->count;
62         for_each_online_cpu(cpu) {
63                 s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
64                 ret += *pcount;
65         }
66         spin_unlock(&fbc->lock);
67         return ret < 0 ? 0 : ret;
68 }
69 EXPORT_SYMBOL(percpu_counter_sum_positive);
70
71 void percpu_counter_init(struct percpu_counter *fbc, s64 amount)
72 {
73         spin_lock_init(&fbc->lock);
74         fbc->count = amount;
75         fbc->counters = alloc_percpu(s32);
76 #ifdef CONFIG_HOTPLUG_CPU
77         mutex_lock(&percpu_counters_lock);
78         list_add(&fbc->list, &percpu_counters);
79         mutex_unlock(&percpu_counters_lock);
80 #endif
81 }
82 EXPORT_SYMBOL(percpu_counter_init);
83
84 void percpu_counter_destroy(struct percpu_counter *fbc)
85 {
86         free_percpu(fbc->counters);
87 #ifdef CONFIG_HOTPLUG_CPU
88         mutex_lock(&percpu_counters_lock);
89         list_del(&fbc->list);
90         mutex_unlock(&percpu_counters_lock);
91 #endif
92 }
93 EXPORT_SYMBOL(percpu_counter_destroy);
94
95 #ifdef CONFIG_HOTPLUG_CPU
96 static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
97                                         unsigned long action, void *hcpu)
98 {
99         unsigned int cpu;
100         struct percpu_counter *fbc;
101
102         if (action != CPU_DEAD)
103                 return NOTIFY_OK;
104
105         cpu = (unsigned long)hcpu;
106         mutex_lock(&percpu_counters_lock);
107         list_for_each_entry(fbc, &percpu_counters, list) {
108                 s32 *pcount;
109
110                 spin_lock(&fbc->lock);
111                 pcount = per_cpu_ptr(fbc->counters, cpu);
112                 fbc->count += *pcount;
113                 *pcount = 0;
114                 spin_unlock(&fbc->lock);
115         }
116         mutex_unlock(&percpu_counters_lock);
117         return NOTIFY_OK;
118 }
119
120 static int __init percpu_counter_startup(void)
121 {
122         hotcpu_notifier(percpu_counter_hotcpu_callback, 0);
123         return 0;
124 }
125 module_init(percpu_counter_startup);
126 #endif