From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753104AbeBLRnK (ORCPT ); Mon, 12 Feb 2018 12:43:10 -0500 Received: from outbound-smtp25.blacknight.com ([81.17.249.193]:39156 "EHLO outbound-smtp25.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751156AbeBLRnJ (ORCPT ); Mon, 12 Feb 2018 12:43:09 -0500 Date: Mon, 12 Feb 2018 17:43:07 +0000 From: Mel Gorman To: Peter Zijlstra Cc: Mike Galbraith , Matt Fleming , LKML Subject: Re: [PATCH 3/4] sched/fair: Do not migrate on wake_affine_weight if weights are equal Message-ID: <20180212174307.ytpc4r2iy7rakh32@techsingularity.net> References: <20180212145857.8056-1-mgorman@techsingularity.net> <20180212145857.8056-4-mgorman@techsingularity.net> <20180212172926.GY25201@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20180212172926.GY25201@hirez.programming.kicks-ass.net> User-Agent: NeoMutt/20170912 (1.9.0) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 12, 2018 at 06:29:26PM +0100, Peter Zijlstra wrote: > On Mon, Feb 12, 2018 at 02:58:56PM +0000, Mel Gorman wrote: > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index c1091cb023c4..28c8d9c91955 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -5747,7 +5747,16 @@ wake_affine_weight(struct sched_domain *sd, struct task_struct *p, > > prev_eff_load *= 100 + (sd->imbalance_pct - 100) / 2; > > prev_eff_load *= capacity_of(this_cpu); > > > > - return this_eff_load <= prev_eff_load ? this_cpu : nr_cpumask_bits; > > + /* > > + * If sync, adjust the weight of prev_eff_load such that if > > + * prev_eff == this_eff that select_idle_sibling will consider > > + * stacking the wakee on top of the waker if no other CPU is > > + * idle. > > + */ > > + if (sync) > > + prev_eff_load += 1; > > So where we had <= and would consistently favour pulling the task to the > waking CPU when all else what equal, you now switch to <, such that when > things are equal we do not pull. > > That makes sense I suppose. > Yep, with the addenum that when CPU load is equal, it does not necessarily mean they are equal in terms of memory locality. It might make more sense to use <= if there were more cases where we stacked tasks on the same CPU but we avoid that as much as possible for good reasons. -- Mel Gorman SUSE Labs