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=-17.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 98E75C4361B for ; Thu, 17 Dec 2020 15:00:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 45953235FD for ; Thu, 17 Dec 2020 15:00:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728156AbgLQPAm (ORCPT ); Thu, 17 Dec 2020 10:00:42 -0500 Received: from mail.kernel.org ([198.145.29.99]:60282 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728118AbgLQPAm (ORCPT ); Thu, 17 Dec 2020 10:00:42 -0500 Date: Thu, 17 Dec 2020 14:59:54 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1608217201; bh=SryEihmoGHKC5r1tLLVQJV4OdHijgIVYH18Si4+ZQUE=; h=From:To:Cc:Subject:References:In-Reply-To:From; b=N22OMxb+xaAjqkpCj4d3MHixRyNQhPXV6rdtIQ15RNVqNQeprGTLVAd20egsnrxJY uOSYgL8oU5NSCqc52q24+/d0n6RFicWy26aoTiR8Ohqb2TMnSA7YqXYaDDA06T3h9R evanQ6FiSR/bOONjtVrKzXXJgMedjO686WaL35XToPghTZB9DrIeuBzUQtJAQqzIqa 43uHKXNHr1PPswqSI592mhRYcyvFB3ppLEhUPpag9ct0eabMRS/H0zmH4RDiCyv+HG ue7W0nBnopnMCer75U/CLVzAxUXfkEQ9tq31m1EgzuxwbwD/J1tZfCQWUm2ZNY4SAq x2wufl1GC+/OA== From: Will Deacon To: Peter Zijlstra Cc: Qais Yousef , linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, Catalin Marinas , Marc Zyngier , Greg Kroah-Hartman , Morten Rasmussen , Suren Baghdasaryan , Quentin Perret , Tejun Heo , Li Zefan , Johannes Weiner , Ingo Molnar , Juri Lelli , Vincent Guittot , kernel-team@android.com Subject: Re: [PATCH v5 07/15] cpuset: Don't use the cpu_possible_mask as a last resort for cgroup v1 Message-ID: <20201217145954.GA17881@willie-the-truck> References: <20201208132835.6151-1-will@kernel.org> <20201208132835.6151-8-will@kernel.org> <20201217121552.ds7g2icvqp5nvtha@e107158-lin.cambridge.arm.com> <20201217134401.GY3040@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201217134401.GY3040@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On Thu, Dec 17, 2020 at 02:44:01PM +0100, Peter Zijlstra wrote: > On Thu, Dec 17, 2020 at 12:15:52PM +0000, Qais Yousef wrote: > > On 12/08/20 13:28, Will Deacon wrote: > > > If the scheduler cannot find an allowed CPU for a task, > > > cpuset_cpus_allowed_fallback() will widen the affinity to cpu_possible_mask > > > if cgroup v1 is in use. > > > > > > In preparation for allowing architectures to provide their own fallback > > > mask, just return early if we're not using cgroup v2 and allow > > > select_fallback_rq() to figure out the mask by itself. > > > > > > Cc: Li Zefan > > > Cc: Tejun Heo > > > Cc: Johannes Weiner > > > Reviewed-by: Quentin Perret > > > Signed-off-by: Will Deacon > > > --- > > > kernel/cgroup/cpuset.c | 6 ++++-- > > > 1 file changed, 4 insertions(+), 2 deletions(-) > > > > > > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c > > > index 57b5b5d0a5fd..e970737c3ed2 100644 > > > --- a/kernel/cgroup/cpuset.c > > > +++ b/kernel/cgroup/cpuset.c > > > @@ -3299,9 +3299,11 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask) > > > > > > void cpuset_cpus_allowed_fallback(struct task_struct *tsk) > > > { > > > + if (!is_in_v2_mode()) > > > + return; /* select_fallback_rq will try harder */ > > > + > > > rcu_read_lock(); > > > - do_set_cpus_allowed(tsk, is_in_v2_mode() ? > > > - task_cs(tsk)->cpus_allowed : cpu_possible_mask); > > > + do_set_cpus_allowed(tsk, task_cs(tsk)->cpus_allowed); > > > > Why is it safe to return that for cpuset v2? > > v1 > > Because in that case it does cpu_possible_mask, which, if you look at > select_fallback_rq(), is exactly what happens when cpuset 'fails' to > find a candidate. > > Or at least, that's how I read the patch. I think Qais a point with v2 though: if task_cs(tsk)->cpus_allowed contains 64-bit-only CPUs, then we're in trouble here. I should be taking the intersection with the task_cpu_possible_mask() for the task. Will