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=-13.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,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 4A244C433E1 for ; Tue, 25 Aug 2020 02:11:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 31F7920578 for ; Tue, 25 Aug 2020 02:11:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726818AbgHYCL1 (ORCPT ); Mon, 24 Aug 2020 22:11:27 -0400 Received: from out30-133.freemail.mail.aliyun.com ([115.124.30.133]:54715 "EHLO out30-133.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725850AbgHYCL1 (ORCPT ); Mon, 24 Aug 2020 22:11:27 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R161e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e01355;MF=xlpang@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0U6n3eMK_1598321483; Received: from xunleideMacBook-Pro.local(mailfrom:xlpang@linux.alibaba.com fp:SMTPD_---0U6n3eMK_1598321483) by smtp.aliyun-inc.com(127.0.0.1); Tue, 25 Aug 2020 10:11:24 +0800 Reply-To: xlpang@linux.alibaba.com Subject: Re: [PATCH] sched/fair: Fix wrong cpu selecting from isolated domain To: Srikar Dronamraju Cc: Ingo Molnar , Peter Zijlstra , Vincent Guittot , Juri Lelli , Wetp Zhang , linux-kernel@vger.kernel.org References: <1598272219-43040-1-git-send-email-xlpang@linux.alibaba.com> <20200824133820.GA31355@linux.vnet.ibm.com> From: xunlei Message-ID: Date: Tue, 25 Aug 2020 10:11:24 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <20200824133820.GA31355@linux.vnet.ibm.com> Content-Type: text/plain; charset=gbk Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/8/24 PM9:38, Srikar Dronamraju wrote: > * Xunlei Pang [2020-08-24 20:30:19]: > >> We've met problems that occasionally tasks with full cpumask >> (e.g. by putting it into a cpuset or setting to full affinity) >> were migrated to our isolated cpus in production environment. >> >> After some analysis, we found that it is due to the current >> select_idle_smt() not considering the sched_domain mask. >> >> Fix it by checking the valid domain mask in select_idle_smt(). >> >> Fixes: 10e2f1acd010 ("sched/core: Rewrite and improve select_idle_siblings()) >> Reported-by: Wetp Zhang >> Signed-off-by: Xunlei Pang >> --- >> kernel/sched/fair.c | 9 +++++---- >> 1 file changed, 5 insertions(+), 4 deletions(-) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index 1a68a05..fa942c4 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -6075,7 +6075,7 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int >> /* >> * Scan the local SMT mask for idle CPUs. >> */ >> -static int select_idle_smt(struct task_struct *p, int target) >> +static int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target) >> { >> int cpu; >> >> @@ -6083,7 +6083,8 @@ static int select_idle_smt(struct task_struct *p, int target) >> return -1; >> >> for_each_cpu(cpu, cpu_smt_mask(target)) { >> - if (!cpumask_test_cpu(cpu, p->cpus_ptr)) >> + if (!cpumask_test_cpu(cpu, p->cpus_ptr) || >> + !cpumask_test_cpu(cpu, sched_domain_span(sd))) >> continue; > > Don't think this is right thing to do. What if this task had set a cpumask > that doesn't cover all the cpus in this sched_domain_span(sd) It doesn't matter, without this patch, it selects an idle cpu from: "cpu_smt_mask(target) and p->cpus_ptr" with this patch, it selects an idle cpu from: "cpu_smt_mask(target) and p->cpus_ptr and sched_domain_span(sd)" > > cpu_smt_mask(target) would already limit to the sched_domain_span(sd) so I > am not sure how this can help? > > Here is an example: CPU0 and CPU16 are hyper-thread pair, CPU16 is domain isolated. So its sd_llc doesn't contain CPU16, and cpu_smt_mask(0) is 0 and 16. Then we have @target is 0, select_idle_smt() may return the isolated(and idle) CPU16 without this patch.