From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755249AbbAVVB2 (ORCPT ); Thu, 22 Jan 2015 16:01:28 -0500 Received: from www.linutronix.de ([62.245.132.108]:33486 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753039AbbAVVB0 (ORCPT ); Thu, 22 Jan 2015 16:01:26 -0500 Date: Thu, 22 Jan 2015 22:00:57 +0100 (CET) From: Thomas Gleixner To: Preeti U Murthy cc: peterz@infradead.org, linuxppc-dev@lists.ozlabs.org, mingo@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH V2] cpuidle: Add missing checks to the exit condition of cpu_idle_poll() In-Reply-To: <20150121105655.15279.59626.stgit@preeti.in.ibm.com> Message-ID: References: <20150121105655.15279.59626.stgit@preeti.in.ibm.com> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001,URIBL_BLOCKED=0.001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 21 Jan 2015, Preeti U Murthy wrote: > cpu_idle_poll() is entered into when either the cpu_idle_force_poll is set or > tick_check_broadcast_expired() returns true. The exit condition from > cpu_idle_poll() is tif_need_resched(). > > However this does not take into account scenarios where cpu_idle_force_poll > changes or tick_check_broadcast_expired() returns false, without setting > the resched flag. So a cpu will be caught in cpu_idle_poll() needlessly, > thereby wasting power. Add an explicit check on cpu_idle_force_poll and > tick_check_broadcast_expired() to the exit condition of cpu_idle_poll() > to avoid this. > > Signed-off-by: Preeti U Murthy Reviewed-by: Thomas Gleixner > --- > Changes from V1: Modified the Changelog > > kernel/sched/idle.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c > index c47fce7..aaf1c1d 100644 > --- a/kernel/sched/idle.c > +++ b/kernel/sched/idle.c > @@ -47,7 +47,8 @@ static inline int cpu_idle_poll(void) > rcu_idle_enter(); > trace_cpu_idle_rcuidle(0, smp_processor_id()); > local_irq_enable(); > - while (!tif_need_resched()) > + while (!tif_need_resched() && > + (cpu_idle_force_poll || tick_check_broadcast_expired())) > cpu_relax(); > trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id()); > rcu_idle_exit(); > >