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