From patchwork Mon May 26 09:16:14 2014 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: preeti X-Patchwork-Id: 4240781 Return-Path: X-Original-To: patchwork-linux-arm@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.19.201]) by patchwork1.web.kernel.org (Postfix) with ESMTP id F12459F1E7 for ; Mon, 26 May 2014 09:24:02 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 2961F20170 for ; Mon, 26 May 2014 09:24:02 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.9]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 53DD72016C for ; Mon, 26 May 2014 09:24:01 +0000 (UTC) Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1Wor5s-0006zF-4X; Mon, 26 May 2014 09:21:20 +0000 Received: from e38.co.us.ibm.com ([32.97.110.159]) by bombadil.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1Wor5o-0006vx-Py for linux-arm-kernel@lists.infradead.org; Mon, 26 May 2014 09:21:17 +0000 Received: from /spool/local by e38.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; Mon, 26 May 2014 03:20:51 -0600 Received: from b03cxnp07029.gho.boulder.ibm.com (b03cxnp07029.gho.boulder.ibm.com [9.17.130.16]) by d03dlp01.boulder.ibm.com (Postfix) with ESMTP id 978911FF003F for ; Mon, 26 May 2014 03:20:50 -0600 (MDT) Received: from d03av06.boulder.ibm.com (d03av06.boulder.ibm.com [9.17.195.245]) by b03cxnp07029.gho.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id s4Q7HVUo7209364 for ; Mon, 26 May 2014 09:17:31 +0200 Received: from d03av06.boulder.ibm.com (loopback [127.0.0.1]) by d03av06.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id s4Q9OlIB004666 for ; Mon, 26 May 2014 03:24:48 -0600 Received: from [9.79.192.190] ([9.79.192.190]) by d03av06.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVin) with ESMTP id s4Q9Ockn004404; Mon, 26 May 2014 03:24:40 -0600 Message-ID: <5383065E.9030601@linux.vnet.ibm.com> Date: Mon, 26 May 2014 14:46:14 +0530 From: Preeti U Murthy User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120717 Thunderbird/14.0 MIME-Version: 1.0 To: Vincent Guittot Subject: Re: [PATCH v2 01/11] sched: fix imbalance flag reset References: <1400860385-14555-1-git-send-email-vincent.guittot@linaro.org> <1400860385-14555-2-git-send-email-vincent.guittot@linaro.org> <5381C70E.3030605@linux.vnet.ibm.com> In-Reply-To: X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14052609-1344-0000-0000-000001CAE76B X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20140526_022116_908350_CF404C26 X-CRM114-Status: GOOD ( 18.84 ) X-Spam-Score: -5.7 (-----) Cc: Nicolas Pitre , "linaro-kernel@lists.linaro.org" , Russell King - ARM Linux , Daniel Lezcano , Peter Zijlstra , Mike Galbraith , linux-kernel , Ingo Molnar , Morten Rasmussen , LAK X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Spam-Status: No, score=-2.5 required=5.0 tests=BAYES_00,RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP On 05/26/2014 01:19 PM, Vincent Guittot wrote: > On 25 May 2014 12:33, Preeti U Murthy wrote: >> Hi Vincent, >> >> On 05/23/2014 09:22 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. >> >> Why do we do active balancing today when there is at-most 1 task on the >> busiest cpu? Shouldn't we be skipping load balancing altogether? If we >> do active balancing when the number of tasks = 1, it will lead to a ping >> pong right? > > That's the purpose of the patch to prevent this useless active load > balance. When the imbalance flag is set, an active load balance is > triggered whatever the load balance is because of pinned tasks that > prevents a balance state. No I mean this: sched:Do not continue load balancing when the busiest cpu has one running task From: Preeti U Murthy --- kernel/sched/fair.c | 2 ++ 1 file changed, 2 insertions(+) } Regards Preeti U Murthy > > Vincent > >> >> Regards >> Preeti U Murthy >> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index c9617b7..b175333 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6626,6 +6626,8 @@ more_balance: } goto out_balanced; } + } else { + goto out; } if (!ld_moved) {