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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C0ECDC433EF for ; Sat, 9 Oct 2021 22:52:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9790460C4B for ; Sat, 9 Oct 2021 22:52:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231183AbhJIWyX (ORCPT ); Sat, 9 Oct 2021 18:54:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57056 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230296AbhJIWyS (ORCPT ); Sat, 9 Oct 2021 18:54:18 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2B6AFC061570 for ; Sat, 9 Oct 2021 15:52:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=HlKWYN2dw8uuQPxr2tgsDfcykAdf/apHp3S9FQkV370=; b=qk9H63EqlV+cMSj2hs8OSZ5oac RtLNYC37cNC862LycoSvAKYfUanYEXUG9Det5ZBNgpP98WCYlwhsERVwlJLbfUYItiX7wzoeLTKVv swRoqZgcvoO5HBHXijyx71h0r+Z2IctlwhtuksO/1HfO1a1Renjx5O9kNvNXseoJV1SJ39QLmDgTI FjIYaG/a1/feq0Z9kTpHvlbt2NHb66HF2Hqfwu2UFnha2CIAFP2FT/7tH5YLMriDErMpk08Yagi/n XlLDvKtXpSySU/KGObNuAejiBxzk/vVmqzao2YoLVwhVS5tPzNnInsm1NEjiz384fomLpIV/lCTwm fdE7z7FQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=worktop.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1mZLBB-004SNm-LJ; Sat, 09 Oct 2021 22:51:09 +0000 Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000) id 414639811D4; Sun, 10 Oct 2021 00:50:57 +0200 (CEST) Date: Sun, 10 Oct 2021 00:50:57 +0200 From: Peter Zijlstra To: Tao Zhou Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira Subject: Re: [PATCH] sched/fair: Check idle_cpu in select_idle_core/cpu() Message-ID: <20211009225057.GB174703@worktop.programming.kicks-ass.net> References: <20211009180941.20458-1-tao.zhou@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211009180941.20458-1-tao.zhou@linux.dev> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Oct 10, 2021 at 02:09:41AM +0800, Tao Zhou wrote: > In select_idle_core(), the idle core returned may have no cpu > allowed. I think the idle core returned for the task is the one > that can be allowed to run. I insist on this semantics. > > In select_idle_cpu(), if select_idle_core() can not find the > idle core, one reason is that the core is not allowed for the > task, but the core itself is idle from the point of > sds->has_idle_cores. I insist on this semantics. > > No others, just two additional check. > --- > kernel/sched/fair.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index f6a05d9b5443..a44aca5095d3 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6213,7 +6213,7 @@ static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpu > *idle_cpu = cpu; > } > > - if (idle) > + if (idle && *idle_cpu != -1) > return core; In that case, core would be nr_cpu_ids (==nr_cpumask_bits), and then the caller checks: (unsigned)i < nr_cpumask_bits > cpumask_andnot(cpus, cpus, cpu_smt_mask(core)); > @@ -6324,7 +6324,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool > } > } > > - if (has_idle_core) > + if (has_idle_core && *idle_cpu != -1) > set_idle_cores(target, false); And this one I'm completely failing, why shouldn't we mark the core as non-idle when there is a single idle CPU found? That's just worng.