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 /*
 141  * Compare counter against given value.
 142  * Return 1 if greater, 0 if equal and -1 if less
 143  */
 144 int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs)
 145 {
 146         s64     count;
 147
 148         count = percpu_counter_read(fbc);
 149         /* Check to see if rough count will be sufficient for comparison */
 150         if (abs(count - rhs) > (percpu_counter_batch*num_online_cpus())) {
 151                 if (count > rhs)
 152                         return 1;
 153                 else
 154                         return -1;
 155         }
 156         /* Need to use precise count */
 157         count = percpu_counter_sum(fbc);
 158         if (count > rhs)
 159                 return 1;
 160         else if (count < rhs)
 161                 return -1;
 162         else
 163                 return 0;
 164 }
 165 EXPORT_SYMBOL(percpu_counter_compare);
 166
 167 static int __init percpu_counter_startup(void)
 168 {
 169         compute_batch_value();
 170         hotcpu_notifier(percpu_counter_hotcpu_callback, 0);
 171         return 0;
 172 }
 173 module_init(percpu_counter_startup);