Merge branch 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel...
[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 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);