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                 *pcount = 0;
  66         }
  67         fbc->count = ret;
  68
  69         spin_unlock(&fbc->lock);
  70         return ret;
  71 }
  72 EXPORT_SYMBOL(__percpu_counter_sum);
  73
  74 static struct lock_class_key percpu_counter_irqsafe;
  75
  76 int percpu_counter_init(struct percpu_counter *fbc, s64 amount)
  77 {
  78         spin_lock_init(&fbc->lock);
  79         fbc->count = amount;
  80         fbc->counters = alloc_percpu(s32);
  81         if (!fbc->counters)
  82                 return -ENOMEM;
  83 #ifdef CONFIG_HOTPLUG_CPU
  84         mutex_lock(&percpu_counters_lock);
  85         list_add(&fbc->list, &percpu_counters);
  86         mutex_unlock(&percpu_counters_lock);
  87 #endif
  88         return 0;
  89 }
  90 EXPORT_SYMBOL(percpu_counter_init);
  91
  92 int percpu_counter_init_irq(struct percpu_counter *fbc, s64 amount)
  93 {
  94         int err;
  95
  96         err = percpu_counter_init(fbc, amount);
  97         if (!err)
  98                 lockdep_set_class(&fbc->lock, &percpu_counter_irqsafe);
  99         return err;
 100 }
 101
 102 void percpu_counter_destroy(struct percpu_counter *fbc)
 103 {
 104         if (!fbc->counters)
 105                 return;
 106
 107         free_percpu(fbc->counters);
 108         fbc->counters = NULL;
 109 #ifdef CONFIG_HOTPLUG_CPU
 110         mutex_lock(&percpu_counters_lock);
 111         list_del(&fbc->list);
 112         mutex_unlock(&percpu_counters_lock);
 113 #endif
 114 }
 115 EXPORT_SYMBOL(percpu_counter_destroy);
 116
 117 #ifdef CONFIG_HOTPLUG_CPU
 118 static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
 119                                         unsigned long action, void *hcpu)
 120 {
 121         unsigned int cpu;
 122         struct percpu_counter *fbc;
 123
 124         if (action != CPU_DEAD)
 125                 return NOTIFY_OK;
 126
 127         cpu = (unsigned long)hcpu;
 128         mutex_lock(&percpu_counters_lock);
 129         list_for_each_entry(fbc, &percpu_counters, list) {
 130                 s32 *pcount;
 131                 unsigned long flags;
 132
 133                 spin_lock_irqsave(&fbc->lock, flags);
 134                 pcount = per_cpu_ptr(fbc->counters, cpu);
 135                 fbc->count += *pcount;
 136                 *pcount = 0;
 137                 spin_unlock_irqrestore(&fbc->lock, flags);
 138         }
 139         mutex_unlock(&percpu_counters_lock);
 140         return NOTIFY_OK;
 141 }
 142
 143 static int __init percpu_counter_startup(void)
 144 {
 145         hotcpu_notifier(percpu_counter_hotcpu_callback, 0);
 146         return 0;
 147 }
 148 module_init(percpu_counter_startup);
 149 #endif