From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751558AbaEIF2Q (ORCPT ); Fri, 9 May 2014 01:28:16 -0400 Received: from mx1.redhat.com ([209.132.183.28]:57957 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750772AbaEIF2P (ORCPT ); Fri, 9 May 2014 01:28:15 -0400 Date: Fri, 9 May 2014 01:27:43 -0400 From: Rik van Riel To: Peter Zijlstra Cc: Mike Galbraith , linux-kernel@vger.kernel.org, morten.rasmussen@arm.com, mingo@kernel.org, george.mccollister@gmail.com, ktkhai@parallels.com Subject: [PATCH] sched: wake up task on prev_cpu if not in SD_WAKE_AFFINE domain with cpu Message-ID: <20140509012743.67d4006d@annuminas.surriel.com> In-Reply-To: <536C3B69.1000208@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> Organization: Red Hat, Inc. MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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... ---8<--- Subject: sched: wake up task on prev_cpu if not in SD_WAKE_AFFINE domain with cpu If prev_cpu and cpu are not part of the same SD_WAKE_AFFINE domain, the current code will fall back to the select_idlest_group CPU selection mechanism, instead of trying to wake up the task on a CPU near its previous CPU. Fix that by always calling select_idle_sibling when doing an SD_BALANCE_WAKE wakeup. Signed-off-by: Rik van Riel --- kernel/sched/fair.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 7570dd9..5d33fb1b 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4452,7 +4452,9 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f if (affine_sd) { if (cpu != prev_cpu && wake_affine(affine_sd, p, sync)) prev_cpu = cpu; + } + if (sd_flag & SD_BALANCE_WAKE) { new_cpu = select_idle_sibling(p, prev_cpu); goto unlock; }