From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arjan van de Ven Subject: [patch] Remove the per cpu tick skew Date: Tue, 27 Jul 2010 21:02:10 -0700 Message-ID: <20100727210210.58d3118c@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: Received: from casper.infradead.org ([85.118.1.10]:34457 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750785Ab0G1ECM (ORCPT ); Wed, 28 Jul 2010 00:02:12 -0400 Sender: linux-arch-owner@vger.kernel.org List-ID: To: linux-kernel@vger.kernel.org Cc: tglx@linutronix.de, linux-arch@vger.kernel.org Hi, the following patch is a win for power management on x86.... ... but since this touches generic code.. are there any other architectures that would be negatively affected by this? Subject: [patch] Remove the per cpu tick skew Historically, Linux has tried to make the regular timer tick on the various CPUs not happen at the same time, to avoid contention on xtime_lock. Nowadays, with the tickless kernel, this contention no longer happens since time keeping and updating are done differently. In addition, this skew is actually hurting power consumption in a measurable way on many-core systems. Signed-off-by: Arjan van de Ven --- linux.trees.git/kernel/time/tick-sched.c~ 2010-07-16 09:40:50.000000000 -0400 +++ linux.trees.git/kernel/time/tick-sched.c 2010-07-26 11:18:51.138003329 -0400 @@ -780,7 +780,6 @@ { struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); ktime_t now = ktime_get(); - u64 offset; /* * Emulate tick processing via per-CPU hrtimers: @@ -790,10 +789,6 @@ /* Get the next period (per cpu) */ hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update()); - offset = ktime_to_ns(tick_period) >> 1; - do_div(offset, num_possible_cpus()); - offset *= smp_processor_id(); - hrtimer_add_expires_ns(&ts->sched_timer, offset); for (;;) { hrtimer_forward(&ts->sched_timer, now, tick_period); -- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org