From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754177AbcEWLMM (ORCPT ); Mon, 23 May 2016 07:12:12 -0400 Received: from mx2.suse.de ([195.135.220.15]:49262 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753480AbcEWLML (ORCPT ); Mon, 23 May 2016 07:12:11 -0400 Message-ID: <1464001927.4537.118.camel@suse.de> Subject: Re: [PATCH 03/16] sched/fair: Disregard idle task wakee_flips in wake_wide From: Mike Galbraith To: Morten Rasmussen , peterz@infradead.org, mingo@redhat.com Cc: dietmar.eggemann@arm.com, yuyang.du@intel.com, vincent.guittot@linaro.org, linux-kernel@vger.kernel.org Date: Mon, 23 May 2016 13:12:07 +0200 In-Reply-To: <1464001138-25063-4-git-send-email-morten.rasmussen@arm.com> References: <1464001138-25063-1-git-send-email-morten.rasmussen@arm.com> <1464001138-25063-4-git-send-email-morten.rasmussen@arm.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.16.5 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2016-05-23 at 11:58 +0100, Morten Rasmussen wrote: > wake_wide() is based on task wakee_flips of the waker and the wakee to > decide whether an affine wakeup is desirable. On lightly loaded systems > the waker is frequently the idle task (pid=0) which can accumulate a lot > of wakee_flips in that scenario. It makes little sense to prevent affine > wakeups on an idle cpu due to the idle task wakee_flips, so it makes > more sense to ignore them in wake_wide(). You sure? What's the difference between a task flipping enough to warrant spreading the load, and an interrupt source doing the same? I've both witnessed firsthand, and received user confirmation of this very thing improving utilization. > cc: Ingo Molnar > cc: Peter Zijlstra > > Signed-off-by: Morten Rasmussen > --- > kernel/sched/fair.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index c49e25a..0fe3020 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -5007,6 +5007,10 @@ static int wake_wide(struct task_struct *p) > unsigned int slave = p->wakee_flips; > int factor = this_cpu_read(sd_llc_size); > > + /* Don't let the idle task prevent affine wakeups */ > + if (is_idle_task(current)) > + return 0; > + > if (master < slave) > swap(master, slave); > if (slave < factor || master < slave * factor)