Messages in this thread Patch in this message | | | Date | Mon, 25 Jun 2007 17:11:15 -0700 | From | Andrew Morton <> | Subject | Re: [patch -mm 09/28] Tick management: spread timer interrupt |
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On Sat, 23 Jun 2007 13:32:34 -0000 Thomas Gleixner <tglx@linutronix.de> wrote:
> From: john stultz <johnstul@us.ibm.com> > > After discussing w/ Thomas over IRC, it seems the issue is the sched > tick fires on every cpu at the same time, causing extra lock contention. > > This smaller change, adds an extra offset per cpu so the ticks don't > line up. This patch also drops the idle latency from 40us down to under > 20us. > > Signed-off-by: john stultz <johnstul@us.ibm.com> > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > > --- > kernel/time/tick-sched.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > Index: linux-2.6.22-rc4-mm/kernel/time/tick-sched.c > =================================================================== > --- linux-2.6.22-rc4-mm.orig/kernel/time/tick-sched.c 2007-06-23 14:38:56.000000000 +0200 > +++ linux-2.6.22-rc4-mm/kernel/time/tick-sched.c 2007-06-23 14:38:58.000000000 +0200 > @@ -573,6 +573,7 @@ void tick_setup_sched_timer(void) > { > struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); > ktime_t now = ktime_get(); > + u64 offset; > > /* > * Emulate tick processing via per-CPU hrtimers: > @@ -581,8 +582,12 @@ void tick_setup_sched_timer(void) > ts->sched_timer.function = tick_sched_timer; > ts->sched_timer.cb_mode = HRTIMER_CB_IRQSAFE_NO_SOFTIRQ; > > - /* Get the next period */ > + /* 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);
With CONFIG_NR_CPUS=128 on a 2-way this'll be a pretty lumpy spreading? Perhaps it woud be better to use num_possible_cpus() here?
> + offset *= smp_processor_id(); > + ts->sched_timer.expires = ktime_add_ns(ts->sched_timer.expires, offset); > > for (;;) { > hrtimer_forward(&ts->sched_timer, now, tick_period); > > -- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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