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         INIT_LIST_HEAD(&fbc->list);
  80         mutex_lock(&percpu_counters_lock);
  81         list_add(&fbc->list, &percpu_counters);
  82         mutex_unlock(&percpu_counters_lock);
  83 #endif
  84         return 0;
  85 }
  86 EXPORT_SYMBOL(__percpu_counter_init);
  87
  88 void percpu_counter_destroy(struct percpu_counter *fbc)
  89 {
  90         if (!fbc->counters)
  91                 return;
  92
  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         free_percpu(fbc->counters);
  99         fbc->counters = NULL;
 100 }
 101 EXPORT_SYMBOL(percpu_counter_destroy);
 102
 103 int percpu_counter_batch __read_mostly = 32;
 104 EXPORT_SYMBOL(percpu_counter_batch);
 105
 106 static void compute_batch_value(void)
 107 {
 108         int nr = num_online_cpus();
 109
 110         percpu_counter_batch = max(32, nr*2);
 111 }
 112
 113 static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
 114                                         unsigned long action, void *hcpu)
 115 {
 116 #ifdef CONFIG_HOTPLUG_CPU
 117         unsigned int cpu;
 118         struct percpu_counter *fbc;
 119
 120         compute_batch_value();
 121         if (action != CPU_DEAD)
 122                 return NOTIFY_OK;
 123
 124         cpu = (unsigned long)hcpu;
 125         mutex_lock(&percpu_counters_lock);
 126         list_for_each_entry(fbc, &percpu_counters, list) {
 127                 s32 *pcount;
 128                 unsigned long flags;
 129
 130                 spin_lock_irqsave(&fbc->lock, flags);
 131                 pcount = per_cpu_ptr(fbc->counters, cpu);
 132                 fbc->count += *pcount;
 133                 *pcount = 0;
 134                 spin_unlock_irqrestore(&fbc->lock, flags);
 135         }
 136         mutex_unlock(&percpu_counters_lock);
 137 #endif
 138         return NOTIFY_OK;
 139 }
 140
 141 /*
 142  * Compare counter against given value.
 143  * Return 1 if greater, 0 if equal and -1 if less
 144  */
 145 int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs)
 146 {
 147         s64     count;
 148
 149         count = percpu_counter_read(fbc);
 150         /* Check to see if rough count will be sufficient for comparison */
 151         if (abs(count - rhs) > (percpu_counter_batch*num_online_cpus())) {
 152                 if (count > rhs)
 153                         return 1;
 154                 else
 155                         return -1;
 156         }
 157         /* Need to use precise count */
 158         count = percpu_counter_sum(fbc);
 159         if (count > rhs)
 160                 return 1;
 161         else if (count < rhs)
 162                 return -1;
 163         else
 164                 return 0;
 165 }
 166 EXPORT_SYMBOL(percpu_counter_compare);
 167
 168 static int __init percpu_counter_startup(void)
 169 {
 170         compute_batch_value();
 171         hotcpu_notifier(percpu_counter_hotcpu_callback, 0);
 172         return 0;
 173 }
 174 module_init(percpu_counter_startup);