From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757530AbcFAH6k (ORCPT ); Wed, 1 Jun 2016 03:58:40 -0400 Received: from mga09.intel.com ([134.134.136.24]:53728 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752089AbcFAH6i (ORCPT ); Wed, 1 Jun 2016 03:58:38 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.26,400,1459839600"; d="scan'208";a="966432328" Date: Wed, 1 Jun 2016 08:01:05 +0800 From: Yuyang Du To: Mike Galbraith Cc: Peter Zijlstra , mingo@kernel.org, linux-kernel@vger.kernel.org, bsegall@google.com, pjt@google.com, morten.rasmussen@arm.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com Subject: Re: [RFC PATCH 1/2] sched: Clean up SD_BALANCE_WAKE flags in sched domain build-up Message-ID: <20160601000105.GU18670@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1464757633.4023.39.camel@gmail.com> 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 07:07:13AM +0200, Mike Galbraith wrote: > On Tue, 2016-05-31 at 09:31 +0800, Yuyang Du wrote: > > On Tue, May 31, 2016 at 11:21:46AM +0200, Peter Zijlstra wrote: > > > On Tue, May 31, 2016 at 09:11:37AM +0800, Yuyang Du wrote: > > > > The SD_BALANCE_WAKE is irrelevant in the contexts of these two removals, > > > > and in addition SD_BALANCE_WAKE is not and should not be set in any > > > > sched_domain flags so far. > > > > > > This Changelog doesn't make any sense... > > > > How? SD_BALANCE_WAKE is not in any sched_domain flags (sd->flags), even if > > it is, it is not used anywhere, no? > > If the user chooses to set SD_BALANCE_WAKE in sd->flags, it is in fact > used. It's just not turned on by default due to full balance on every > wakeup being far too painful to do by default. 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.