From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758000AbcFAJAf (ORCPT ); Wed, 1 Jun 2016 05:00:35 -0400 Received: from mga01.intel.com ([192.55.52.88]:58005 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757442AbcFAJA3 (ORCPT ); Wed, 1 Jun 2016 05:00:29 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.26,400,1459839600"; d="scan'208";a="712112882" Date: Wed, 1 Jun 2016 09:03:11 +0800 From: Yuyang Du To: Vincent Guittot Cc: Mike Galbraith , Peter Zijlstra , Ingo Molnar , linux-kernel , Benjamin Segall , Paul Turner , Morten Rasmussen , Dietmar Eggemann Subject: Re: [RFC PATCH 1/2] sched: Clean up SD_BALANCE_WAKE flags in sched domain build-up Message-ID: <20160601010311.GV18670@intel.com> References: <1464657098-24880-1-git-send-email-yuyang.du@intel.com> <1464657098-24880-2-git-send-email-yuyang.du@intel.com> <20160531092146.GT3192@twins.programming.kicks-ass.net> <20160531013132.GQ18670@intel.com> <1464757633.4023.39.camel@gmail.com> <20160601000105.GU18670@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Wed, Jun 01, 2016 at 10:32:53AM +0200, Vincent Guittot wrote: > > Yup. Up to this point, we don't have any disagreement. And I don't think we > > have any disagreement conceptually. What the next patch really does is: > > > > (1) we don't remove SD_BALANCE_WAKE as an important sched_domain flag, on > > the contrary, we strengthen it. > > > > (2) the semantic of SD_BALANCE_WAKE is currently represented by SD_WAKE_AFFINE, > > we actually remove this representation. > > > > (3) regarding the semantic of SD_WAKE_AFFINE, it is really not about selecting > > waker CPU or about the fast path. Conceptually, it is just saying the waker > > CPU is a valid and important candidate if SD_BALANCE_WAKE, which is just so > > obvious, so I don't think it deserves to be a separate sched_domain flag. > > > > (4) the outcome is, if SD_BALANCE_WAKE, we definitely will/should try waker CPU, > > and if !SD_BALANCE_WAKE, we don't try waker CPU. So nothing functional is > > changed. > > > AFAIU, there is 4 possible cases during wake up: > - we don't want any balance at wake so we don't have SD_BALANCE_WAKE > nor SD_WAKE_AFFINE in sched_domain->flags > - we only want wake affine balance check so we only have > SD_WAKE_AFFINE in sched_domain->flags > - we want wake_affine and full load balance at wake so we have both > SD_BALANCE_WAKE and SD_WAKE_AFFINE in sched_domain->flags > - we want full load balance but want to skip wake affine fast path so > we only have SD_BALANCE_WAKE in sched_domain->flags > > I'm not sure that we can still do only wake_affine or only full > load_balance with your changes whereas these sequences are valid ones So with the patch, we will have a little bit semantic change, SD_BALANCE_WAKE implies SD_WAKE_AFFINE if allowed, and will favor "fast path" if possible. I don't think we should do anything otherwise. So I think this is a combined case better than either of the "only wake_affine" or "only full" cases. Make sense?