Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758025AbaDXO7g (ORCPT ); Thu, 24 Apr 2014 10:59:36 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:57051 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757361AbaDXO7d (ORCPT ); Thu, 24 Apr 2014 10:59:33 -0400 Date: Thu, 24 Apr 2014 16:59:25 +0200 From: Peter Zijlstra To: Morten Rasmussen Cc: Jason Low , "mingo@kernel.org" , "linux-kernel@vger.kernel.org" , "daniel.lezcano@linaro.org" , "alex.shi@linaro.org" , "preeti@linux.vnet.ibm.com" , "efault@gmx.de" , "vincent.guittot@linaro.org" , "aswin@hp.com" , "chegu_vinod@hp.com" Subject: Re: [PATCH 3/3] sched, fair: Stop searching for tasks in newidle balance if there are runnable tasks Message-ID: <20140424145925.GA27561@twins.programming.kicks-ass.net> References: <1398303035-18255-1-git-send-email-jason.low2@hp.com> <1398303035-18255-4-git-send-email-jason.low2@hp.com> <20140424103059.GL2500@e103034-lin> <20140424113231.GR11096@twins.programming.kicks-ass.net> <20140424140802.GM2500@e103034-lin> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140424140802.GM2500@e103034-lin> 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 On Thu, Apr 24, 2014 at 03:08:02PM +0100, Morten Rasmussen wrote: > On Thu, Apr 24, 2014 at 12:32:31PM +0100, Peter Zijlstra wrote: > > On Thu, Apr 24, 2014 at 11:30:59AM +0100, Morten Rasmussen wrote: > > > On Thu, Apr 24, 2014 at 02:30:35AM +0100, Jason Low wrote: > > > > @@ -6704,7 +6703,12 @@ static int idle_balance(struct rq *this_rq) > > > > interval = msecs_to_jiffies(sd->balance_interval); > > > > if (time_after(next_balance, sd->last_balance + interval)) > > > > next_balance = sd->last_balance + interval; > > > > - if (pulled_task) > > > > + > > > > + /* > > > > + * Stop searching for tasks to pull if there are > > > > + * now runnable tasks on this rq. > > > > + */ > > > > + if (pulled_task || this_rq->nr_running > 0) > > > > > > Should this be cfs tasks instead? > > > > > > + if (pulled_task || this_rq->cfs.h_nr_running > 0) > > > > > > 3.15-rc2 commit 35805ff8f4fc535ac85330170d3c56829c87c677 seems to > > > indicate that using rq->nr_running may lead to trouble. > > > > > > The other two patches look good to me. > > > > No, this really wants to be nr_running, we want to bail the idle > > balancer when there's anything runnable present. > > > > Note how out: is very careful to return -1 (which results in RETRY_TASK) > > when rq->nr_running != rq->cfs.h_nr_running. > > > > That same out: test also makes problem that commit fixes impossible > > again. > > I should have done my homework properly. I may be missing something, but > don't we risk bailing out of idle balance if there is a throttled rt > task and go straight to idle? Good point, depends, in tip/sched/core Kirill fixed that. For -linus this is indeed a problem. See patches: 46383648b3c7 sched: Revert commit 4c6c4e38c4e9 ("sched/core: Fix endless loop in pick_next_task()") f4ebcbc0d7e0 sched/rt: Substract number of tasks of throttled queues from rq->nr_running 653d07a6989a sched/rt: Add accessors rq_of_rt_se() 22abdef37ceb sched/rt: Sum number of all children tasks in hierarhy at ->rt_nr_running So for sched/core everything should be fine. This does mean I have to queue this patch for /core and not /urgent (/me quickly moves). -- 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/