From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760112AbXFWNYu (ORCPT ); Sat, 23 Jun 2007 09:24:50 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758093AbXFWNWH (ORCPT ); Sat, 23 Jun 2007 09:22:07 -0400 Received: from www.osadl.org ([213.239.205.134]:59225 "EHLO mail.tglx.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1757393AbXFWNWC (ORCPT ); Sat, 23 Jun 2007 09:22:02 -0400 Message-Id: <20070623124030.531042944@inhelltoy.tec.linutronix.de> References: <20070623124005.931747831@inhelltoy.tec.linutronix.de> User-Agent: quilt/0.46-1 Date: Sat, 23 Jun 2007 13:32:34 -0000 From: Thomas Gleixner To: Andrew Morton Cc: Andi Kleen , Ingo Molnar , Arjan van de Ven , Venkatesh Pallipadi , John Stultz , Chris Wright , LKML Subject: [patch -mm 09/28] Tick management: spread timer interrupt Content-Disposition: inline; filename=tick-spread-timer-interrupts.patch Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org From: john stultz 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 Signed-off-by: Thomas Gleixner --- 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); + 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); --