From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758023AbcFAJgq (ORCPT ); Wed, 1 Jun 2016 05:36:46 -0400 Received: from mail-wm0-f50.google.com ([74.125.82.50]:35630 "EHLO mail-wm0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757490AbcFAJgn (ORCPT ); Wed, 1 Jun 2016 05:36:43 -0400 Message-ID: <1464773799.4023.72.camel@gmail.com> Subject: Re: [RFC PATCH 1/2] sched: Clean up SD_BALANCE_WAKE flags in sched domain build-up From: Mike Galbraith To: Yuyang Du 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 Date: Wed, 01 Jun 2016 11:36:39 +0200 In-Reply-To: <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> <20160601000105.GU18670@intel.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 Wed, 2016-06-01 at 08:01 +0800, Yuyang Du wrote: > 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. Nope, those two have different meanings. We pass SD_BALANCE_WAKE to identify a ttwu() wakeup, just as we pass SD_BALANCE_FORK to say we're waking a child. SD_WAKE_AFFINE means exactly what it says, but is only applicable to ttwu() wakeups. > (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. SD_WAKE_AFFINE being a separate domain flag, the user can turn it on/off... separately :) > (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. If wake_wide() says we do not want an affine wakeup, but you apply SD_WAKE_AFFINE meaning to SD_BALANCE_WAKE and turn it on in ->flags, we'll give the user a free sample of full balance cost, no? -Mike