From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753025AbbCXP1L (ORCPT ); Tue, 24 Mar 2015 11:27:11 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:51618 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752179AbbCXP1J (ORCPT ); Tue, 24 Mar 2015 11:27:09 -0400 Date: Tue, 24 Mar 2015 16:26:55 +0100 From: Peter Zijlstra To: Morten Rasmussen Cc: mingo@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, yuyang.du@intel.com, preeti@linux.vnet.ibm.com, mturquette@linaro.org, nico@linaro.org, rjw@rjwysocki.net, juri.lelli@arm.com, linux-kernel@vger.kernel.org Subject: Re: [RFCv3 PATCH 44/48] sched: Tipping point from energy-aware to conventional load balancing Message-ID: <20150324152655.GT23123@twins.programming.kicks-ass.net> References: <1423074685-6336-1-git-send-email-morten.rasmussen@arm.com> <1423074685-6336-45-git-send-email-morten.rasmussen@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1423074685-6336-45-git-send-email-morten.rasmussen@arm.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 04, 2015 at 06:31:21PM +0000, Morten Rasmussen wrote: > From: Dietmar Eggemann > > Energy-aware load balancing bases on cpu usage so the upper bound of its > operational range is a fully utilized cpu. Above this tipping point it > makes more sense to use weighted_cpuload to preserve smp_nice. > This patch implements the tipping point detection in update_sg_lb_stats > as if one cpu is over-utilized the current energy-aware load balance > operation will fall back into the conventional weighted load based one. > > cc: Ingo Molnar > cc: Peter Zijlstra > > Signed-off-by: Dietmar Eggemann > --- > kernel/sched/fair.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 6b79603..4849bad 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6723,6 +6723,10 @@ static inline void update_sg_lb_stats(struct lb_env *env, > sgs->sum_weighted_load += weighted_cpuload(i); > if (idle_cpu(i)) > sgs->idle_cpus++; > + > + /* If cpu is over-utilized, bail out of ea */ > + if (env->use_ea && cpu_overutilized(i, env->sd)) > + env->use_ea = false; > } I don't immediately see why this is desired. Why would a single overloaded CPU be reason to quit? It could be the cpus simply aren't 'balanced' right and the group as a whole is still under utilized. In that case we want to continue the balance pass to reach this equilibrium.