From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751826AbcEYJ0t (ORCPT ); Wed, 25 May 2016 05:26:49 -0400 Received: from foss.arm.com ([217.140.101.70]:33434 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750857AbcEYJ0r (ORCPT ); Wed, 25 May 2016 05:26:47 -0400 Date: Wed, 25 May 2016 10:27:27 +0100 From: Morten Rasmussen To: Yuyang Du Cc: peterz@infradead.org, mingo@redhat.com, dietmar.eggemann@arm.com, vincent.guittot@linaro.org, mgalbraith@suse.de, linux-kernel@vger.kernel.org Subject: Re: [PATCH 07/16] sched: Make SD_BALANCE_WAKE a topology flag Message-ID: <20160525092727.GK27946@e105550-lin.cambridge.arm.com> References: <1464001138-25063-1-git-send-email-morten.rasmussen@arm.com> <1464001138-25063-8-git-send-email-morten.rasmussen@arm.com> <20160524235249.GH18670@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160524235249.GH18670@intel.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, May 25, 2016 at 07:52:49AM +0800, Yuyang Du wrote: > On Mon, May 23, 2016 at 11:58:49AM +0100, Morten Rasmussen wrote: > > For systems with the SD_ASYM_CPUCAPACITY flag set on higher level in the > > sched_domain hierarchy we need a way to enable wake-up balancing for the > > lower levels as well as we may want to balance tasks that don't fit the > > capacity of the previous cpu. > > > > We have the option of introducing a new topology flag to express this > > requirement, or let the existing SD_BALANCE_WAKE flag be set by the > > architecture as a topology flag. The former means introducing yet > > another flag, the latter breaks the current meaning of topology flags. > > None of the options are really desirable. > > I'd propose to replace SD_WAKE_AFFINE with SD_BALANCE_WAKE. And the > SD_WAKE_AFFINE semantic is simply "waker allowed": > > waker_allowed = cpumask_test_cpu(cpu, tsk_cpus_allowed(p)); > > This can be implemented without current functionality change. > > From there, the choice between waker and wakee, and fast path > select_idle_sibling() and the rest slow path should be reworked, which > I am thinking about. I don't really understand how that would work. If you change the semantics of the flags you don't preserve current behaviour. To me it sounds like at total rewrite of everything. SD_BALANCE_WAKE controls whether we go slow path or not in case want_affine is false. SD_WAKE_AFFINE controls whether we should consider waking up near the waker instead of always waking up near the previous cpu.