Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753143AbaGIDGh (ORCPT ); Tue, 8 Jul 2014 23:06:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:31619 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751104AbaGIDGg (ORCPT ); Tue, 8 Jul 2014 23:06:36 -0400 Message-ID: <53BCB170.9020005@redhat.com> Date: Tue, 08 Jul 2014 23:05:20 -0400 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 MIME-Version: 1.0 To: Vincent Guittot , peterz@infradead.org, mingo@kernel.org, linux-kernel@vger.kernel.org, linux@arm.linux.org.uk, linux-arm-kernel@lists.infradead.org CC: preeti@linux.vnet.ibm.com, Morten.Rasmussen@arm.com, efault@gmx.de, nicolas.pitre@linaro.org, linaro-kernel@lists.linaro.org, daniel.lezcano@linaro.org, dietmar.eggemann@arm.com Subject: Re: [PATCH v3 01/12] sched: fix imbalance flag reset References: <1404144343-18720-1-git-send-email-vincent.guittot@linaro.org> <1404144343-18720-2-git-send-email-vincent.guittot@linaro.org> In-Reply-To: <1404144343-18720-2-git-send-email-vincent.guittot@linaro.org> X-Enigmail-Version: 1.6 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 06/30/2014 12:05 PM, Vincent Guittot wrote: > The imbalance flag can stay set whereas there is no imbalance. > > Let assume that we have 3 tasks that run on a dual cores /dual > cluster system. We will have some idle load balance which are > triggered during tick. Unfortunately, the tick is also used to > queue background work so we can reach the situation where short > work has been queued on a CPU which already runs a task. The load > balance will detect this imbalance (2 tasks on 1 CPU and an idle > CPU) and will try to pull the waiting task on the idle CPU. The > waiting task is a worker thread that is pinned on a CPU so an > imbalance due to pinned task is detected and the imbalance flag is > set. Then, we will not be able to clear the flag because we have at > most 1 task on each CPU but the imbalance flag will trig to useless > active load balance between the idle CPU and the busy CPU. > > We need to reset of the imbalance flag as soon as we have reached a > balanced state. > > Signed-off-by: Vincent Guittot Acked-by: Rik van Riel - -- All rights reversed -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEcBAEBAgAGBQJTvLFvAAoJEM553pKExN6DUcYIAJkj0fl4DIpx/7ywqSSCo4Da 1IpJI5Hz2zb+NunG8M/4kugDSYvMmiuNhFgG1ET7me11jxTcTqg0e8UZ4zJbW55u i14IVyXLW+AVhJNQc1Umu3c6tTnjawOIzLa4wJ5JCVFVTj/5AhHyJjbKfQJnew1q XlYm8+FPGmXQgJ0G3itmpx3gAYsrQIQXtIhM9wwgmKiysF4s+HZZppyZKtGbOtm4 ia408LsmjOYYp4vGSTa4F4IWx1K0fJVpz33TsCLb2pwKy6t/4hKf9tOn/wXPSLVc NbWrP7zYYJ8EaXgo/RV9OJnPXq0h0Tbp9eMtd4u/hRCrcHw1dUZBpDMIRkS5NzI= =uoh0 -----END PGP SIGNATURE----- -- 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/