Commit c67ad917 authored by Andrew Morton's avatar Andrew Morton Committed by Linus Torvalds
Browse files

percpu_counters(): use cpu notifiers 



per-cpu counters presently must iterate over all possible CPUs in the
exhaustive percpu_counter_sum().

But it can be much better to only iterate over the presently-online CPUs.  To
do this, we must arrange for an offlined CPU's count to be spilled into the
counter's central count.

We can do this for all percpu_counters in the machine by linking them into a
single global list and walking that list at CPU_DEAD time.

(I hope.  Might have race windows in which the percpu_counter_sum() count is
inaccurate?)

Cc: Gautham R Shenoy <ego@in.ibm.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 85420cca

include/linux/percpu_counter.h

+6 −12
Original line number Diff line number Diff line
@@ -8,6 +8,7 @@ 


#include <linux/spinlock.h>

#include <linux/smp.h>

#include <linux/list.h>

#include <linux/threads.h>

#include <linux/percpu.h>

#include <linux/types.h>
@@ -17,6 +18,9 @@ 
struct percpu_counter {

	spinlock_t lock;

	s64 count;

#ifdef CONFIG_HOTPLUG_CPU

	struct list_head list;	/* All percpu_counters are on a list */

#endif

	s32 *counters;

};
@@ -26,18 +30,8 @@ struct percpu_counter { 
#define FBC_BATCH	(NR_CPUS*4)

#endif



static inline void percpu_counter_init(struct percpu_counter *fbc, s64 amount)

{

	spin_lock_init(&fbc->lock);

	fbc->count = amount;

	fbc->counters = alloc_percpu(s32);

}



static inline void percpu_counter_destroy(struct percpu_counter *fbc)

{

	free_percpu(fbc->counters);

}



void percpu_counter_init(struct percpu_counter *fbc, s64 amount);

void percpu_counter_destroy(struct percpu_counter *fbc);

void percpu_counter_mod(struct percpu_counter *fbc, s32 amount);

s64 percpu_counter_sum(struct percpu_counter *fbc);

lib/percpu_counter.c

+66 −0
Original line number Diff line number Diff line
@@ -3,8 +3,17 @@ 
 */



#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_mod(struct percpu_counter *fbc, s32 amount)

{

	long count;
@@ -44,3 +53,60 @@ s64 percpu_counter_sum(struct percpu_counter *fbc) 
	return ret < 0 ? 0 : ret;

}

EXPORT_SYMBOL(percpu_counter_sum);



void percpu_counter_init(struct percpu_counter *fbc, s64 amount)

{

	spin_lock_init(&fbc->lock);

	fbc->count = amount;

	fbc->counters = alloc_percpu(s32);

#ifdef CONFIG_HOTPLUG_CPU

	mutex_lock(&percpu_counters_lock);

	list_add(&fbc->list, &percpu_counters);

	mutex_unlock(&percpu_counters_lock);

#endif

}

EXPORT_SYMBOL(percpu_counter_init);



void percpu_counter_destroy(struct percpu_counter *fbc)

{

	free_percpu(fbc->counters);

#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;



		spin_lock(&fbc->lock);

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

		fbc->count += *pcount;

		*pcount = 0;

		spin_unlock(&fbc->lock);

	}

	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

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