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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 143D0C4361A for ; Fri, 4 Dec 2020 13:49:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D8D9C22B2D for ; Fri, 4 Dec 2020 13:49:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730260AbgLDNtN (ORCPT ); Fri, 4 Dec 2020 08:49:13 -0500 Received: from mga12.intel.com ([192.55.52.136]:12386 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725973AbgLDNtM (ORCPT ); Fri, 4 Dec 2020 08:49:12 -0500 IronPort-SDR: gcr7abefRjnqAxZkgkDZLOnp5uWj74cSa7bqbG6pqiAZYw/AvkyA2KZe+dL/333wBhbP/vTr/h PWAItkhOBpbQ== X-IronPort-AV: E=McAfee;i="6000,8403,9824"; a="152629183" X-IronPort-AV: E=Sophos;i="5.78,392,1599548400"; d="scan'208";a="152629183" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Dec 2020 05:47:31 -0800 IronPort-SDR: HKFrPCutvknAwCPutKZjTFkx6BG4NNjKJ/C5v9occZc3p4I0QzvlOCXWrnkUykzi0glEAKGklY HUW7PYPNqv7Q== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.78,392,1599548400"; d="scan'208";a="374350206" Received: from cli6-desk1.ccr.corp.intel.com (HELO [10.239.161.125]) ([10.239.161.125]) by FMSMGA003.fm.intel.com with ESMTP; 04 Dec 2020 05:47:29 -0800 Subject: Re: [PATCH 06/10] sched/fair: Clear the target CPU from the cpumask of CPUs searched From: "Li, Aubrey" To: Vincent Guittot , Mel Gorman Cc: LKML , Barry Song , Ingo Molnar , Peter Ziljstra , Juri Lelli , Valentin Schneider , Linux-ARM References: <20201203141124.7391-1-mgorman@techsingularity.net> <20201203141124.7391-7-mgorman@techsingularity.net> <20201203175204.GY3371@techsingularity.net> <20201204113030.GZ3371@techsingularity.net> <3d8a6d19-afac-dc93-127d-da6505402cdf@linux.intel.com> Message-ID: Date: Fri, 4 Dec 2020 21:47:28 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: <3d8a6d19-afac-dc93-127d-da6505402cdf@linux.intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/12/4 21:40, Li, Aubrey wrote: > On 2020/12/4 21:17, Vincent Guittot wrote: >> On Fri, 4 Dec 2020 at 14:13, Vincent Guittot wrote: >>> >>> On Fri, 4 Dec 2020 at 12:30, Mel Gorman wrote: >>>> >>>> On Fri, Dec 04, 2020 at 11:56:36AM +0100, Vincent Guittot wrote: >>>>>> The intent was that the sibling might still be an idle candidate. In >>>>>> the current draft of the series, I do not even clear this so that the >>>>>> SMT sibling is considered as an idle candidate. The reasoning is that if >>>>>> there are no idle cores then an SMT sibling of the target is as good an >>>>>> idle CPU to select as any. >>>>> >>>>> Isn't the purpose of select_idle_smt ? >>>>> >>>> >>>> Only in part. >>>> >>>>> select_idle_core() looks for an idle core and opportunistically saves >>>>> an idle CPU candidate to skip select_idle_cpu. In this case this is >>>>> useless loops for select_idle_core() because we are sure that the core >>>>> is not idle >>>>> >>>> >>>> If select_idle_core() finds an idle candidate other than the sibling, >>>> it'll use it if there is no idle core -- it picks a busy sibling based >>>> on a linear walk of the cpumask. Similarly, select_idle_cpu() is not >>> >>> My point is that it's a waste of time to loop the sibling cpus of >>> target in select_idle_core because it will not help to find an idle >>> core. The sibling cpus will then be check either by select_idle_cpu >>> of select_idle_smt >> >> also, while looping the cpumask, the sibling cpus of not idle cpu are >> removed and will not be check >> > > IIUC, select_idle_core and select_idle_cpu share the same cpumask(select_idle_mask)? > If the target's sibling is removed from select_idle_mask from select_idle_core(), > select_idle_cpu() will lose the chance to pick it up? aha, no, select_idle_mask will be re-assigned in select_idle_cpu() by: cpumask_and(cpus, sds_idle_cpus(sd->shared), p->cpus_ptr); So, yes, I guess we can remove the cpu_smt_mask(target) from select_idle_core() safely. > > Thanks, > -Aubrey >