From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756818AbaEIPYM (ORCPT ); Fri, 9 May 2014 11:24:12 -0400 Received: from mail-ee0-f48.google.com ([74.125.83.48]:64900 "EHLO mail-ee0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751067AbaEIPYL (ORCPT ); Fri, 9 May 2014 11:24:11 -0400 Message-ID: <1399649042.31219.47.camel@marge.simpson.net> Subject: Re: [PATCH] sched: wake up task on prev_cpu if not in SD_WAKE_AFFINE domain with cpu From: Mike Galbraith To: Rik van Riel Cc: Peter Zijlstra , linux-kernel@vger.kernel.org, morten.rasmussen@arm.com, mingo@kernel.org, george.mccollister@gmail.com, ktkhai@parallels.com Date: Fri, 09 May 2014 17:24:02 +0200 In-Reply-To: <536CE48E.2060305@redhat.com> 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> <536CE48E.2060305@redhat.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2014-05-09 at 10:22 -0400, Rik van Riel wrote: > 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... If no ->flags & SD_BALANCE_WAKE is encountered during traversal, sd remains NULL, we fall through to return prev_cpu. -Mike