Use num_possible_cpus() instead of NR_CPUS for timer distribution
authorjohn stultz <johnstul@us.ibm.com>
Wed, 17 Oct 2007 06:27:18 +0000 (23:27 -0700)
committerLinus Torvalds <torvalds@woody.linux-foundation.org>
Wed, 17 Oct 2007 15:42:53 +0000 (08:42 -0700)
To avoid lock contention, we distribute the sched_timer calls across the
cpus so they do not trigger at the same instant.  However, I used NR_CPUS,
which can cause needless grouping on small smp systems depending on your
kernel config.  This patch converts to using num_possible_cpus() so we
spread it as evenly as possible on every machine.

Briefly tested w/ NR_CPUS=255 and verified reduced contention.

Signed-off-by: John Stultz <johnstul@us.ibm.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
kernel/time/tick-sched.c

index 8c3fef1db09ccb03507a89de6cbd7971dd803f41..ce89ffb474d0cbeba8b2d84af5c3a6c9ae5f7389 100644 (file)
@@ -570,7 +570,7 @@ void tick_setup_sched_timer(void)
        /* Get the next period (per cpu) */
        ts->sched_timer.expires = tick_init_jiffy_update();
        offset = ktime_to_ns(tick_period) >> 1;
-       do_div(offset, NR_CPUS);
+       do_div(offset, num_possible_cpus());
        offset *= smp_processor_id();
        ts->sched_timer.expires = ktime_add_ns(ts->sched_timer.expires, offset);