From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 61306C34031 for ; Wed, 19 Feb 2020 02:46:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 392B624654 for ; Wed, 19 Feb 2020 02:46:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="key not found in DNS" (0-bit key) header.d=mg.codeaurora.org header.i=@mg.codeaurora.org header.b="M5Ob83ha" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728231AbgBSCqY (ORCPT ); Tue, 18 Feb 2020 21:46:24 -0500 Received: from mail27.static.mailgun.info ([104.130.122.27]:25949 "EHLO mail27.static.mailgun.info" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728031AbgBSCqX (ORCPT ); Tue, 18 Feb 2020 21:46:23 -0500 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1582080383; h=In-Reply-To: Content-Type: MIME-Version: References: Message-ID: Subject: Cc: To: From: Date: Sender; bh=EZldwMwfRwILNbyiADsIQMw6OSHJxtFM2DQb2VA7DkY=; b=M5Ob83haVinyvmzduiwwULsSncmmzfQGSn69/7tF0qe9eVWrVdiiKoMedBoxb8LjjFQwZLcW Ebb6VOj1rmYwMtHlu1z40Gm9nKijAgBjyK/jV4aGLzyKtwrw0FgE1j5Y9m+qPhoPahzwQ/+i 0rXKyW5SNqGU6i2pgwyaVk6kffo= X-Mailgun-Sending-Ip: 104.130.122.27 X-Mailgun-Sid: WyI0MWYwYSIsICJsaW51eC1rZXJuZWxAdmdlci5rZXJuZWwub3JnIiwgImJlOWU0YSJd Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by mxa.mailgun.org with ESMTP id 5e4ca178.7fe21eea3ae8-smtp-out-n02; Wed, 19 Feb 2020 02:46:16 -0000 (UTC) Received: by smtp.codeaurora.org (Postfix, from userid 1001) id 076E4C447A0; Wed, 19 Feb 2020 02:46:16 +0000 (UTC) Received: from codeaurora.org (blr-c-bdr-fw-01_GlobalNAT_AllZones-Outside.qualcomm.com [103.229.19.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: pkondeti) by smtp.codeaurora.org (Postfix) with ESMTPSA id 2B682C43383; Wed, 19 Feb 2020 02:46:11 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 2B682C43383 Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; spf=none smtp.mailfrom=pkondeti@codeaurora.org Date: Wed, 19 Feb 2020 08:16:09 +0530 From: Pavan Kondeti To: Qais Yousef Cc: Ingo Molnar , Peter Zijlstra , Steven Rostedt , Dietmar Eggemann , Juri Lelli , Vincent Guittot , Ben Segall , Mel Gorman , linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/3] sched/rt: fix pushing unfit tasks to a better CPU Message-ID: <20200219024608.GE28029@codeaurora.org> References: <20200214163949.27850-1-qais.yousef@arm.com> <20200214163949.27850-4-qais.yousef@arm.com> <20200217092329.GC28029@codeaurora.org> <20200217135306.cjc2225wdlwqiicu@e107158-lin.cambridge.arm.com> <20200218041620.GD28029@codeaurora.org> <20200218174718.ma6cpr2qwnueertn@e107158-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200218174718.ma6cpr2qwnueertn@e107158-lin.cambridge.arm.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 18, 2020 at 05:47:19PM +0000, Qais Yousef wrote: > On 02/18/20 09:46, Pavan Kondeti wrote: > > The original RT task placement i.e without capacity awareness, places the task > > on the previous CPU if the task can preempt the running task. I interpreted it > > as that "higher prio RT" task should get better treatment even if it results > > in stopping the lower prio RT execution and migrating it to another CPU. > > > > Now coming to your patch (merged), we force find_lowest_rq() if the previous > > CPU can't fit the task though this task can right away run there. When the > > lowest mask returns an unfit CPU (with your new patch), We have two choices, > > either to place it on this unfit CPU (may involve migration) or place it on > > the previous CPU to avoid the migration. We are selecting the first approach. > > > > The task_cpu(p) check in find_lowest_rq() only works when the previous CPU > > does not have a RT task. If it is running a lower prio RT task than the > > waking task, the lowest_mask may not contain the previous CPU. > > > > I don't if any workload hurts due to this change in behavior. So not sure > > if we have to restore the original behavior. Something like below will do. > > Is this patch equivalent to yours? If yes, then I got you. If not, then I need > to re-read this again.. > > diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c > index ace9acf9d63c..854a0c9a7be6 100644 > --- a/kernel/sched/rt.c > +++ b/kernel/sched/rt.c > @@ -1476,6 +1476,13 @@ select_task_rq_rt(struct task_struct *p, int cpu, int sd_flag, int flags) > if (test || !rt_task_fits_capacity(p, cpu)) { > int target = find_lowest_rq(p); > > + /* > + * Bail out if we were forcing a migration to find a better > + * fitting CPU but our search failed. > + */ > + if (!test && !rt_task_fits_capacity(p, target)) > + goto out_unlock; > + Yes. This is what I was referring to. Thanks, Pavan -- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.