Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753928Ab3IYHx4 (ORCPT ); Wed, 25 Sep 2013 03:53:56 -0400 Received: from merlin.infradead.org ([205.233.59.134]:40120 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751070Ab3IYHxz (ORCPT ); Wed, 25 Sep 2013 03:53:55 -0400 Date: Wed, 25 Sep 2013 09:53:41 +0200 From: Peter Zijlstra To: Ingo Molnar Cc: Mike Galbraith , Paul Turner , Rik van Riel , linux-kernel@vger.kernel.org Subject: [RFC][PATCH] sched: Avoid select_idle_sibling() for wake_affine(.sync=true) Message-ID: <20130925075341.GB3081@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1416 Lines: 41 Subject: sched: Avoid select_idle_sibling() for wake_affine(.sync=true) From: Peter Zijlstra Date: Wed Sep 25 08:28:39 CEST 2013 When a task is the only running task and does a sync wakeup; avoid going through select_idle_sibling() as it doesn't know the current CPU is going to be idle shortly. Without this two sync wakers will ping-pong between CPUs for no reason. Suggested-by: Rik van Riel Signed-off-by: Peter Zijlstra --- kernel/sched/fair.c | 10 ++++++++++ 1 file changed, 10 insertions(+) --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3461,6 +3461,16 @@ select_task_rq_fair(struct task_struct * if (cpu != prev_cpu && wake_affine(affine_sd, p, sync)) prev_cpu = cpu; + /* + * Don't bother with select_idle_sibling() in the case of a sync wakeup + * where we know the only running task will soon go away. Going + * through select_idle_sibling will only lead to pointless ping-pong. + */ + if (sync && prev_cpu == cpu && cpu_rq(cpu)->nr_running == 1) { + new_cpu = cpu; + goto unlock; + } + new_cpu = select_idle_sibling(p, prev_cpu); goto unlock; } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/