From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757826Ab2HJIOz (ORCPT ); Fri, 10 Aug 2012 04:14:55 -0400 Received: from mailout-de.gmx.net ([213.165.64.22]:48243 "HELO mailout-de.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1757700Ab2HJIOt (ORCPT ); Fri, 10 Aug 2012 04:14:49 -0400 X-Authenticated: #14349625 X-Provags-ID: V01U2FsdGVkX1/KGopRgmTKAj9VmSDpZpRNEFIPGqw/LfYRcIbKEs /BYmfHr/t3y6rc Message-ID: <1344586484.4330.24.camel@marge.simpson.net> Subject: Re: [RFC/PATCH] sched: Honor sync wake up in select_idle_sibling From: Mike Galbraith To: Namhyung Kim Cc: Ingo Molnar , Peter Zijlstra , LKML , Namhyung Kim , Suresh Siddha Date: Fri, 10 Aug 2012 10:14:44 +0200 In-Reply-To: <1344583512-25352-1-git-send-email-namhyung@kernel.org> References: <1344583512-25352-1-git-send-email-namhyung@kernel.org> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 X-Y-GMX-Trusted: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2012-08-10 at 16:25 +0900, Namhyung Kim wrote: > From: Namhyung Kim > > When sync wakeup happens and there's the waker task running alone, > select the target cpu as if it's already idle. Ouch. That defeats the purpose of select_idle_sibling(). Just because we're doing a sync wakeup does not mean there's no convertible overlap, nor that the waker is really really going to take a nap immediately. A lot of the places that benefit up to and including hugely from looking for an idle shared cache to wake to do sync wakeups. > Cc: Mike Galbraith > Cc: Suresh Siddha > Signed-off-by: Namhyung Kim > --- > kernel/sched/fair.c | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index d0cc03b3e70b..64b68bc82b52 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -2632,7 +2632,7 @@ find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu) > /* > * Try and locate an idle CPU in the sched_domain. > */ > -static int select_idle_sibling(struct task_struct *p, int target) > +static int select_idle_sibling(struct task_struct *p, int target, int sync) > { > int cpu = smp_processor_id(); > int prev_cpu = task_cpu(p); > @@ -2646,6 +2646,13 @@ static int select_idle_sibling(struct task_struct *p, int target) > return cpu; > > /* > + * If the task is going to be woken-up on this cpu and there's only > + * the sync-waker running, then it is the right target. > + */ > + if (target == cpu && sync && this_rq()->nr_running == 1) > + return cpu; > + > + /* > * If the task is going to be woken-up on the cpu where it previously > * ran and if it is currently idle, then it the right target. > */ > @@ -2748,7 +2755,7 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags) > if (cpu == prev_cpu || wake_affine(affine_sd, p, sync)) > prev_cpu = cpu; > > - new_cpu = select_idle_sibling(p, prev_cpu); > + new_cpu = select_idle_sibling(p, prev_cpu, sync); > goto unlock; > } >