From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757533AbbCCRMq (ORCPT ); Tue, 3 Mar 2015 12:12:46 -0500 Received: from mail-wi0-f174.google.com ([209.85.212.174]:46291 "EHLO mail-wi0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756224AbbCCRMj (ORCPT ); Tue, 3 Mar 2015 12:12:39 -0500 Date: Tue, 3 Mar 2015 18:12:31 +0100 From: Frederic Weisbecker To: Rik van Riel Cc: peterz@infradead.org, lcapitulino@redhat.com, linux-kernel@vger.kernel.org, mtosatti@redhat.com, mingo@kernel.org, fweisbec@redhat.com Subject: Re: [PATCH] sched,rt,nohz: stop scheduler tick if running realtime task Message-ID: <20150303171227.GB26830@lerouge> References: <20150216152349.6a8ed824@annuminas.surriel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150216152349.6a8ed824@annuminas.surriel.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 16, 2015 at 03:23:49PM -0500, Rik van Riel wrote: > If the CPU is running a realtime task that does not round-robin with > another realtime task of equal priority, there is no point in keeping > the scheduler tick going. After all, whenever the scheduler tick runs, > the kernel will just decide not to reschedule. > > Extend sched_can_stop_tick to recognize these situations, and inform > the rest of the kernel that the scheduler tick can be stopped. > > Signed-off-by: Rik van Riel > Tested-by: Luiz Capitulino > --- > kernel/sched/core.c | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index ade2958a9197..ad985a632c4d 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -745,6 +745,22 @@ static inline bool got_nohz_idle_kick(void) > bool sched_can_stop_tick(void) > { > /* > + * FIFO realtime policy runs the highest priority task. Other runnable > + * tasks are of a lower priority. The scheduler tick does nothing. > + */ > + if (current->policy == SCHED_FIFO) > + return true; > + > + /* > + * Round-robin realtime tasks time slice with other tasks at the same > + * realtime priority. Is this task the only one at this priority? > + */ > + if (current->policy == SCHED_RR) { > + struct sched_rt_entity *rt_se = ¤t->rt; > + return rt_se->run_list.prev == rt_se->run_list.next; > + } > + > + /* I think it should work yes. There are still many things, that the tick updates, which are broken without it (rq->rt_avg is supposed to be updated avery tick for example) but it goes way beyond the scope of this change since SCHED_FIFO tasks are already allowed to stop the tick when no SCHED_OTHER task is running so the problem is there already before this patch. So it's a welcome fix, thanks. > * More than one running task need preemption. > * nr_running update is assumed to be visible > * after IPI is sent from wakers. > -- > 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/