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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 66C76C388F9 for ; Wed, 21 Oct 2020 14:31:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 04C552224E for ; Wed, 21 Oct 2020 14:31:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2441679AbgJUOb6 (ORCPT ); Wed, 21 Oct 2020 10:31:58 -0400 Received: from foss.arm.com ([217.140.110.172]:36012 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2441648AbgJUOb6 (ORCPT ); Wed, 21 Oct 2020 10:31:58 -0400 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 AF398D6E; Wed, 21 Oct 2020 07:31:57 -0700 (PDT) Received: from e107158-lin (e107158-lin.cambridge.arm.com [10.1.194.78]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5E3783F66B; Wed, 21 Oct 2020 07:31:56 -0700 (PDT) Date: Wed, 21 Oct 2020 15:31:53 +0100 From: Qais Yousef To: Morten Rasmussen Cc: Catalin Marinas , Marc Zyngier , linux-arch@vger.kernel.org, Will Deacon , "Peter Zijlstra (Intel)" , Greg Kroah-Hartman , James Morse , Linus Torvalds , linux-arm-kernel@lists.infradead.org Subject: Re: [RFC PATCH v2 4/4] arm64: Export id_aar64fpr0 via sysfs Message-ID: <20201021143153.7ef7n7gdd42l4rbc@e107158-lin> References: <20201021104611.2744565-1-qais.yousef@arm.com> <20201021104611.2744565-5-qais.yousef@arm.com> <63fead90e91e08a1b173792b06995765@kernel.org> <20201021121559.GB3976@gaia> <20201021133316.GF8004@e123083-lin> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20201021133316.GF8004@e123083-lin> Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On 10/21/20 15:33, Morten Rasmussen wrote: > On Wed, Oct 21, 2020 at 01:15:59PM +0100, Catalin Marinas wrote: > > one, though not as easy as automatic task placement by the scheduler (my > > first preference, followed by the id_* regs and the aarch32 mask, though > > not a strong preference for any). > > Automatic task placement by the scheduler would mean giving up the > requirement that the user-space affinity mask must always be honoured. > Is that on the table? > > Killing aarch32 tasks with an empty intersection between the user-space > mask and aarch32_mask is not really "automatic" and would require the > aarch32 capability to be exposed anyway. I just noticed this nasty corner case too. Documentation/admin-guide/cgroup-v1/cpusets.rst: Section 1.9 "If such a task had been bound to some subset of its cpuset using the sched_setaffinity() call, the task will be allowed to run on any CPU allowed in its new cpuset, negating the effect of the prior sched_setaffinity() call." So user space must put the tasks into a valid cpuset to fix the problem. Or make the scheduler behave like the affinity is associated with a cpuset. Can user space put the task into the correct cpuset without a race? Clone3 syscall learnt to specify a cgroup to attach to when forking. Should we do the same for execve()? Thanks -- Qais Yousef