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Date: Wed, 3 Sep 2014 14:49:32 +0200 From: Vincent Guittot <vincent.guittot@...aro.org> To: Preeti U Murthy <preeti@...ux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>, linux-kernel <linux-kernel@...r.kernel.org>, Russell King - ARM Linux <linux@....linux.org.uk>, LAK <linux-arm-kernel@...ts.infradead.org>, Rik van Riel <riel@...hat.com>, Morten Rasmussen <Morten.Rasmussen@....com>, Mike Galbraith <efault@....de>, Nicolas Pitre <nicolas.pitre@...aro.org>, "linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>, Daniel Lezcano <daniel.lezcano@...aro.org>, Dietmar Eggemann <dietmar.eggemann@....com> Subject: Re: [PATCH v5 08/12] sched: move cfs task on a CPU with higher capacity On 3 September 2014 14:26, Preeti U Murthy <preeti@...ux.vnet.ibm.com> wrote: > On 09/03/2014 05:14 PM, Vincent Guittot wrote: >> On 3 September 2014 11:11, Preeti U Murthy <preeti@...ux.vnet.ibm.com> wrote: >>> On 09/01/2014 02:15 PM, Vincent Guittot wrote: [snip] >>> >>> Ok I understand your explanation above. But I was wondering if you would >>> need to add this check around rq->cfs.h_nr_running >= 1 in the above two >>> cases as well. >> >> yes you're right for the test if (rq->nr_running >= 2). >> >> It's not so straight forward for nr_busy_cpus which reflects how many >> CPUs have not stopped their tick. The scheduler assumes that the >> latter are busy with cfs tasks >> >>> >>> I have actually raised this concern over whether we should be using >>> rq->nr_running or cfs_rq->nr_running while we do load balancing in reply >>> to your patch3. While all our load measurements are about the cfs_rq >> >> I have just replied to your comments on patch 3. Sorry for the delay >> >>> load, we use rq->nr_running, which may include tasks from other sched >>> classes as well. We divide them to get average load per task during load >>> balancing which is wrong, isn't it? Similarly during nohz_kick_needed(), >>> we trigger load balancing based on rq->nr_running again. >>> >>> In this patch too, even if you know that the cpu is being dominated by >>> tasks that do not belong to cfs class, you would be triggering a futile >>> load balance if there are no fair tasks to move. >> This patch adds one additional condition that is based on >> rq->cfs.h_nr_running so it should not trigger any futile load balance. >> Then, I have also take advantage of this patch to clean up >> nohz_kick_needed as proposed by Peter but the conditions are the same >> than previously (except the one with rq->cfs.h_nr_running) >> >> I can prepare another patchset that will solve the concerns that you >> raised for nohz_kick_needed and in patch 3 but i would prefer not >> include them in this patchset which is large enough and which subject >> is a bit different. >> Does it seem ok for you ? > > Sure Vincent, thanks! I have in fact sent out a mail raising my concern > over rq->nr_running. If others agree on the issue to be existing, maybe > we can work on this next patchset that can clean this up in all places > necessary and not just in nohz_kick_needed(). Ok, let continue this discussion on the other thread Regards, Vincent > > Regards > Preeti U Murthy >> >> Regards, >> Vincent >>> >>> Regards >>> Preeti U Murthy >>> >> > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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