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percpu_counters(): use cpu notifiers

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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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andrew Morton
2007-07-15 23:39:51 -07:00
committed by Linus Torvalds
parent 85420ccad1
commit c67ad917cb
2 changed files with 72 additions and 12 deletions
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18
include/linux/percpu_counter.h
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@ -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);