/*
   * 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>
  #include <linux/debugobjects.h>
  
  #ifdef CONFIG_HOTPLUG_CPU
  static LIST_HEAD(percpu_counters);
  static DEFINE_SPINLOCK(percpu_counters_lock);
  #endif
  
  #ifdef CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER
  
  static struct debug_obj_descr percpu_counter_debug_descr;
  
  static int percpu_counter_fixup_free(void *addr, enum debug_obj_state state)
  {
  	struct percpu_counter *fbc = addr;
  
  	switch (state) {
  	case ODEBUG_STATE_ACTIVE:
  		percpu_counter_destroy(fbc);
  		debug_object_free(fbc, &percpu_counter_debug_descr);
  		return 1;
  	default:
  		return 0;
  	}
  }
  
  static struct debug_obj_descr percpu_counter_debug_descr = {
  	.name		= "percpu_counter",
  	.fixup_free	= percpu_counter_fixup_free,
  };
  
  static inline void debug_percpu_counter_activate(struct percpu_counter *fbc)
  {
  	debug_object_init(fbc, &percpu_counter_debug_descr);
  	debug_object_activate(fbc, &percpu_counter_debug_descr);
  }
  
  static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc)
  {
  	debug_object_deactivate(fbc, &percpu_counter_debug_descr);
  	debug_object_free(fbc, &percpu_counter_debug_descr);
  }
  
  #else	/* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */
  static inline void debug_percpu_counter_activate(struct percpu_counter *fbc)
  { }
  static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc)
  { }
  #endif	/* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */
  
  void percpu_counter_set(struct percpu_counter *fbc, s64 amount)
  {
  	int cpu;
  	unsigned long flags;
  
  	raw_spin_lock_irqsave(&fbc->lock, flags);
  	for_each_possible_cpu(cpu) {
  		s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
  		*pcount = 0;
  	}
  	fbc->count = amount;
  	raw_spin_unlock_irqrestore(&fbc->lock, flags);
  }
  EXPORT_SYMBOL(percpu_counter_set);
  
  void __percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch)
  {
  	s64 count;
  
  	preempt_disable();
  	count = __this_cpu_read(*fbc->counters) + amount;
  	if (count >= batch || count <= -batch) {
  		unsigned long flags;
  		raw_spin_lock_irqsave(&fbc->lock, flags);
  		fbc->count += count;
  		__this_cpu_sub(*fbc->counters, count - amount);
  		raw_spin_unlock_irqrestore(&fbc->lock, flags);
  	} else {
  		this_cpu_add(*fbc->counters, amount);
  	}
  	preempt_enable();
  }
  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;
  	unsigned long flags;
  
  	raw_spin_lock_irqsave(&fbc->lock, flags);
  	ret = fbc->count;
  	for_each_online_cpu(cpu) {
  		s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
  		ret += *pcount;
  	}
  	raw_spin_unlock_irqrestore(&fbc->lock, flags);
  	return ret;
  }
  EXPORT_SYMBOL(__percpu_counter_sum);
  
  int __percpu_counter_init(struct percpu_counter *fbc, s64 amount,
  			  struct lock_class_key *key)
  {
  	raw_spin_lock_init(&fbc->lock);
  	lockdep_set_class(&fbc->lock, key);
  	fbc->count = amount;
  	fbc->counters = alloc_percpu(s32);
  	if (!fbc->counters)
  		return -ENOMEM;
  
  	debug_percpu_counter_activate(fbc);
  
  #ifdef CONFIG_HOTPLUG_CPU
  	INIT_LIST_HEAD(&fbc->list);
  	spin_lock(&percpu_counters_lock);
  	list_add(&fbc->list, &percpu_counters);
  	spin_unlock(&percpu_counters_lock);
  #endif
  	return 0;
  }
  EXPORT_SYMBOL(__percpu_counter_init);
  
  void percpu_counter_destroy(struct percpu_counter *fbc)
  {
  	if (!fbc->counters)
  		return;
  
  	debug_percpu_counter_deactivate(fbc);
  
  #ifdef CONFIG_HOTPLUG_CPU
  	spin_lock(&percpu_counters_lock);
  	list_del(&fbc->list);
  	spin_unlock(&percpu_counters_lock);
  #endif
  	free_percpu(fbc->counters);
  	fbc->counters = NULL;
  }
  EXPORT_SYMBOL(percpu_counter_destroy);
  
  int percpu_counter_batch __read_mostly = 32;
  EXPORT_SYMBOL(percpu_counter_batch);
  
  static void compute_batch_value(void)
  {
  	int nr = num_online_cpus();
  
  	percpu_counter_batch = max(32, nr*2);
  }
  
  static int percpu_counter_hotcpu_callback(struct notifier_block *nb,
  					unsigned long action, void *hcpu)
  {
  #ifdef CONFIG_HOTPLUG_CPU
  	unsigned int cpu;
  	struct percpu_counter *fbc;
  
  	compute_batch_value();
  	if (action != CPU_DEAD && action != CPU_DEAD_FROZEN)
  		return NOTIFY_OK;
  
  	cpu = (unsigned long)hcpu;
  	spin_lock(&percpu_counters_lock);
  	list_for_each_entry(fbc, &percpu_counters, list) {
  		s32 *pcount;
  		unsigned long flags;
  
  		raw_spin_lock_irqsave(&fbc->lock, flags);
  		pcount = per_cpu_ptr(fbc->counters, cpu);
  		fbc->count += *pcount;
  		*pcount = 0;
  		raw_spin_unlock_irqrestore(&fbc->lock, flags);
  	}
  	spin_unlock(&percpu_counters_lock);
  #endif
  	return NOTIFY_OK;
  }
  
  /*
   * Compare counter against given value.
   * Return 1 if greater, 0 if equal and -1 if less
   */
  int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs)
  {
  	s64	count;
  
  	count = percpu_counter_read(fbc);
  	/* Check to see if rough count will be sufficient for comparison */
  	if (abs(count - rhs) > (percpu_counter_batch*num_online_cpus())) {
  		if (count > rhs)
  			return 1;
  		else
  			return -1;
  	}
  	/* Need to use precise count */
  	count = percpu_counter_sum(fbc);
  	if (count > rhs)
  		return 1;
  	else if (count < rhs)
  		return -1;
  	else
  		return 0;
  }
  EXPORT_SYMBOL(percpu_counter_compare);
  
  static int __init percpu_counter_startup(void)
  {
  	compute_batch_value();
  	hotcpu_notifier(percpu_counter_hotcpu_callback, 0);
  	return 0;
  }
  module_init(percpu_counter_startup);