From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756698AbaEIOWo (ORCPT ); Fri, 9 May 2014 10:22:44 -0400 Received: from mx1.redhat.com ([209.132.183.28]:15763 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756457AbaEIOWk (ORCPT ); Fri, 9 May 2014 10:22:40 -0400 Message-ID: <536CE48E.2060305@redhat.com> Date: Fri, 09 May 2014 10:22:06 -0400 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.4.0 MIME-Version: 1.0 To: Mike Galbraith CC: Peter Zijlstra , linux-kernel@vger.kernel.org, morten.rasmussen@arm.com, mingo@kernel.org, george.mccollister@gmail.com, ktkhai@parallels.com Subject: Re: [PATCH] sched: wake up task on prev_cpu if not in SD_WAKE_AFFINE domain with cpu References: <20140502004237.79dd3de6@annuminas.surriel.com> <1399011219.5233.55.camel@marge.simpson.net> <53633B81.1080403@redhat.com> <1399016273.5233.94.camel@marge.simpson.net> <536379D0.8070306@redhat.com> <1399030032.5233.142.camel@marge.simpson.net> <5363B793.9010208@redhat.com> <20140506115448.GH11096@twins.programming.kicks-ass.net> <536943C9.4030502@redhat.com> <20140506203916.GQ17778@laptop.programming.kicks-ass.net> <536C3B69.1000208@redhat.com> <20140509012743.67d4006d@annuminas.surriel.com> <1399620873.5200.68.camel@marge.simpson.net> In-Reply-To: <1399620873.5200.68.camel@marge.simpson.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/09/2014 03:34 AM, Mike Galbraith wrote: > On Fri, 2014-05-09 at 01:27 -0400, Rik van Riel wrote: >> On Thu, 08 May 2014 22:20:25 -0400 >> Rik van Riel wrote: >> >>> Looks like SD_BALANCE_WAKE is not gotten from the sd flags at >>> all, but passed into select_task_rq by try_to_wake_up, as a >>> hard coded sd_flags argument. >> >>> Should we do that, if SD_WAKE_BALANCE is not set for any sched domain? >> >> I answered my own question. The sd_flag SD_WAKE_BALANCE simply means >> "this is a wakeup of a previously existing task, please place it >> properly". >> >> However, it appears that the current code will fall back to the large >> loop with select_idlest_group and friends, if prev_cpu and cpu are not >> part of the same SD_WAKE_AFFINE sched domain. That is a bug... > > ttwu(): cpu = select_task_rq(p, p->wake_cpu, SD_BALANCE_WAKE, wake_flags); > > We pass SD_BALANCE_WAKE for a normal wakeup, so sd will only be set if > we encounter a domain during traversal where Joe User has told us to do > (expensive) wake balancing before we hit a domain shared by waker/wakee. > > The user can turn SD_WAKE_AFFINE off beyond socket, and we'll not pull > cross node on wakeup. > > Or, you could create an override button to say despite SD_WAKE_AFFINE > perhaps having been set during domain construction (because of some > pseudo-random numbers), don't do that if we have a preferred node, or > just make that automatically part of having numa scheduling enabled, and > don't bother wasting cycles if preferred && this != preferred. That's not the problem. The problem is that if we do not do an affine wakeup, due to SD_WAKE_AFFINE not being set on a top level domain, we will not try to run p on prev_cpu, but we will fall through into the loop with find_idlest_group, etc... -- All rights reversed