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(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;
  68 }
  69 EXPORT_SYMBOL(__percpu_counter_sum);
  70
  71 int 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         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         free_percpu(fbc->counters);
  93 #ifdef CONFIG_HOTPLUG_CPU
  94         mutex_lock(&percpu_counters_lock);
  95         list_del(&fbc->list);
  96         mutex_unlock(&percpu_counters_lock);
  97 #endif
  98 }
  99 EXPORT_SYMBOL(percpu_counter_destroy);
 100
 101 #ifdef CONFIG_HOTPLUG_CPU
 102 static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
 103                                         unsigned long action, void *hcpu)
 104 {
 105         unsigned int cpu;
 106         struct percpu_counter *fbc;
 107
 108         if (action != CPU_DEAD)
 109                 return NOTIFY_OK;
 110
 111         cpu = (unsigned long)hcpu;
 112         mutex_lock(&percpu_counters_lock);
 113         list_for_each_entry(fbc, &percpu_counters, list) {
 114                 s32 *pcount;
 115
 116                 spin_lock(&fbc->lock);
 117                 pcount = per_cpu_ptr(fbc->counters, cpu);
 118                 fbc->count += *pcount;
 119                 *pcount = 0;
 120                 spin_unlock(&fbc->lock);
 121         }
 122         mutex_unlock(&percpu_counters_lock);
 123         return NOTIFY_OK;
 124 }
 125
 126 static int __init percpu_counter_startup(void)
 127 {
 128         hotcpu_notifier(percpu_counter_hotcpu_callback, 0);
 129         return 0;
 130 }
 131 module_init(percpu_counter_startup);
 132 #endif