From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754877AbcEWOJ6 (ORCPT ); Mon, 23 May 2016 10:09:58 -0400 Received: from foss.arm.com ([217.140.101.70]:51433 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754453AbcEWOJ5 (ORCPT ); Mon, 23 May 2016 10:09:57 -0400 Date: Mon, 23 May 2016 15:10:36 +0100 From: Morten Rasmussen To: Mike Galbraith Cc: peterz@infradead.org, mingo@redhat.com, dietmar.eggemann@arm.com, yuyang.du@intel.com, vincent.guittot@linaro.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 03/16] sched/fair: Disregard idle task wakee_flips in wake_wide Message-ID: <20160523141035.GC27946@e105550-lin.cambridge.arm.com> References: <1464001138-25063-1-git-send-email-morten.rasmussen@arm.com> <1464001138-25063-4-git-send-email-morten.rasmussen@arm.com> <1464001927.4537.118.camel@suse.de> <20160523120010.GB27946@e105550-lin.cambridge.arm.com> <1464008446.4537.130.camel@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1464008446.4537.130.camel@suse.de> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 23, 2016 at 03:00:46PM +0200, Mike Galbraith wrote: > On Mon, 2016-05-23 at 13:00 +0100, Morten Rasmussen wrote: > > > The problem then seems to be distinguishing truly idle and busy doing > > interrupts. The issue that I observe is that wake_wide() likes pushing > > tasks around in lightly scenarios which isn't desirable for power > > management. Selecting the same cpu again may potentially let others > > reach deeper C-state. > > > > With that in mind I will if I can do better. Suggestions are welcome :-) > > None here. For big boxen that are highly idle, you'd likely want to > shut down nodes and consolidate load, but otoh, all that slows response > to burst, which I hate. I prefer race to idle, let power gating do its > job. If I had a server farm with enough capacity vs load variability > to worry about, I suspect I'd become highly interested in routing. I don't disagree for systems of that scale, but at the other end of the spectrum it is a single SoC we are trying squeeze the best possible mileage out of. That implies optimizing for power gating to reach deeper C-states when possible by consolidating idle-time and grouping idle cpus. Migrating task unnecessarily isn't helping us in achieving that, unfortunately :-(