/*
   * Fast batching percpu counters.
   */
  
  #include <linux/percpu_counter.h>

  #include <linux/notifier.h>
  #include <linux/mutex.h>
  #include <linux/init.h>
  #include <linux/cpu.h>

  #include <linux/module.h>

  #ifdef CONFIG_HOTPLUG_CPU
  static LIST_HEAD(percpu_counters);
  static DEFINE_MUTEX(percpu_counters_lock);
  #endif

  void percpu_counter_set(struct percpu_counter *fbc, s64 amount)
  {
  	int cpu;
  
  	spin_lock(&fbc->lock);
  	for_each_possible_cpu(cpu) {
  		s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
  		*pcount = 0;
  	}
  	fbc->count = amount;
  	spin_unlock(&fbc->lock);
  }
  EXPORT_SYMBOL(percpu_counter_set);

  void __percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch)

  {

  	s64 count;

  	s32 *pcount;

  	int cpu = get_cpu();
  
  	pcount = per_cpu_ptr(fbc->counters, cpu);
  	count = *pcount + amount;

  	if (count >= batch || count <= -batch) {

  		spin_lock(&fbc->lock);
  		fbc->count += count;
  		*pcount = 0;
  		spin_unlock(&fbc->lock);
  	} else {
  		*pcount = count;
  	}
  	put_cpu();
  }

  EXPORT_SYMBOL(__percpu_counter_add);

  
  /*
   * Add up all the per-cpu counts, return the result.  This is a more accurate
   * but much slower version of percpu_counter_read_positive()
   */

  s64 __percpu_counter_sum(struct percpu_counter *fbc)

  {

  	s64 ret;

  	int cpu;
  
  	spin_lock(&fbc->lock);
  	ret = fbc->count;

  	for_each_online_cpu(cpu) {

  		s32 *pcount = per_cpu_ptr(fbc->counters, cpu);

  		ret += *pcount;

  		*pcount = 0;

  	}

  	fbc->count = ret;

  	spin_unlock(&fbc->lock);

  	return ret;

  }

  EXPORT_SYMBOL(__percpu_counter_sum);

  static struct lock_class_key percpu_counter_irqsafe;

  int percpu_counter_init(struct percpu_counter *fbc, s64 amount)

  {
  	spin_lock_init(&fbc->lock);
  	fbc->count = amount;
  	fbc->counters = alloc_percpu(s32);

  	if (!fbc->counters)
  		return -ENOMEM;

  #ifdef CONFIG_HOTPLUG_CPU
  	mutex_lock(&percpu_counters_lock);
  	list_add(&fbc->list, &percpu_counters);
  	mutex_unlock(&percpu_counters_lock);
  #endif

  	return 0;

  }
  EXPORT_SYMBOL(percpu_counter_init);

  
  int percpu_counter_init_irq(struct percpu_counter *fbc, s64 amount)
  {
  	int err;
  
  	err = percpu_counter_init(fbc, amount);
  	if (!err)
  		lockdep_set_class(&fbc->lock, &percpu_counter_irqsafe);
  	return err;
  }

  
  void percpu_counter_destroy(struct percpu_counter *fbc)
  {

  	if (!fbc->counters)
  		return;

  	free_percpu(fbc->counters);

  	fbc->counters = NULL;

  #ifdef CONFIG_HOTPLUG_CPU
  	mutex_lock(&percpu_counters_lock);
  	list_del(&fbc->list);
  	mutex_unlock(&percpu_counters_lock);
  #endif
  }
  EXPORT_SYMBOL(percpu_counter_destroy);
  
  #ifdef CONFIG_HOTPLUG_CPU
  static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb,
  					unsigned long action, void *hcpu)
  {
  	unsigned int cpu;
  	struct percpu_counter *fbc;
  
  	if (action != CPU_DEAD)
  		return NOTIFY_OK;
  
  	cpu = (unsigned long)hcpu;
  	mutex_lock(&percpu_counters_lock);
  	list_for_each_entry(fbc, &percpu_counters, list) {
  		s32 *pcount;

  		unsigned long flags;

  		spin_lock_irqsave(&fbc->lock, flags);

  		pcount = per_cpu_ptr(fbc->counters, cpu);
  		fbc->count += *pcount;
  		*pcount = 0;

  		spin_unlock_irqrestore(&fbc->lock, flags);

  	}
  	mutex_unlock(&percpu_counters_lock);
  	return NOTIFY_OK;
  }
  
  static int __init percpu_counter_startup(void)
  {
  	hotcpu_notifier(percpu_counter_hotcpu_callback, 0);
  	return 0;
  }
  module_init(percpu_counter_startup);
  #endif