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=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 DB35EC433DB for ; Sun, 7 Mar 2021 18:20:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A9F7F650F2 for ; Sun, 7 Mar 2021 18:20:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230480AbhCGSUA (ORCPT ); Sun, 7 Mar 2021 13:20:00 -0500 Received: from foss.arm.com ([217.140.110.172]:54594 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230425AbhCGSTu (ORCPT ); Sun, 7 Mar 2021 13:19:50 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 67A9ED6E; Sun, 7 Mar 2021 10:19:50 -0800 (PST) Received: from e113632-lin (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id EC2C93F73C; Sun, 7 Mar 2021 10:19:48 -0800 (PST) From: Valentin Schneider To: "Song Bao Hua \(Barry Song\)" , "vincent.guittot\@linaro.org" , "mingo\@redhat.com" , "peterz\@infradead.org" , "juri.lelli\@redhat.com" , "dietmar.eggemann\@arm.com" , "rostedt\@goodmis.org" , "bsegall\@google.com" , "mgorman\@suse.de" Cc: "linux-kernel\@vger.kernel.org" , "linuxarm\@openeuler.org" Subject: RE: [PATCH] sched/topology: remove redundant cpumask_and in init_overlap_sched_group In-Reply-To: <27e60cb105e040deb16af774399db15e@hisilicon.com> References: <20210304222944.32504-1-song.bao.hua@hisilicon.com> <27e60cb105e040deb16af774399db15e@hisilicon.com> User-Agent: Notmuch/0.21 (http://notmuchmail.org) Emacs/26.3 (x86_64-pc-linux-gnu) Date: Sun, 07 Mar 2021 18:19:43 +0000 Message-ID: MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/03/21 20:25, Song Bao Hua (Barry Song) wrote: >> -----Original Message----- >> From: Valentin Schneider [mailto:valentin.schneider@arm.com] >> Sent: Saturday, March 6, 2021 12:49 AM >> To: Song Bao Hua (Barry Song) ; >> vincent.guittot@linaro.org; mingo@redhat.com; peterz@infradead.org; >> juri.lelli@redhat.com; dietmar.eggemann@arm.com; rostedt@goodmis.org; >> bsegall@google.com; mgorman@suse.de >> Cc: linux-kernel@vger.kernel.org; linuxarm@openeuler.org; Song Bao Hua (Barry >> Song) >> Subject: Re: [PATCH] sched/topology: remove redundant cpumask_and in >> init_overlap_sched_group >> >> On 05/03/21 11:29, Barry Song wrote: >> > mask is built in build_balance_mask() by for_each_cpu(i, sg_span), so >> > it must be a subset of sched_group_span(sg). >> >> So we should indeed have >> >> cpumask_subset(sched_group_span(sg), mask) >> >> but that doesn't imply >> >> cpumask_first(sched_group_span(sg)) == cpumask_first(mask) >> >> does it? I'm thinking if in your topology of N CPUs, CPUs 0 and N-1 are the >> furthest away, you will most likely hit > > It is true: > cpumask_first(sched_group_span(sg)) != cpumask_first(mask) > > but > > cpumask_first_and(sched_group_span(sg), mask) = cpumask_first(mask) > > since mask is always subset of sched_group_span(sg). > You're right, I read it the wrong way around, sorry about that. Reviewed-by: Valentin Schneider