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=-0.8 required=3.0 tests=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 7B471C35242 for ; Fri, 14 Feb 2020 20:28:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 48D02222C4 for ; Fri, 14 Feb 2020 20:28:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730085AbgBNU2b (ORCPT ); Fri, 14 Feb 2020 15:28:31 -0500 Received: from Galois.linutronix.de ([193.142.43.55]:56210 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726191AbgBNU2b (ORCPT ); Fri, 14 Feb 2020 15:28:31 -0500 Received: from p5b06da22.dip0.t-ipconnect.de ([91.6.218.34] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1j2hZa-0006Uc-4K; Fri, 14 Feb 2020 21:28:26 +0100 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id 98825101304; Fri, 14 Feb 2020 21:28:25 +0100 (CET) From: Thomas Gleixner To: Peter Xu , linux-kernel@vger.kernel.org Cc: Ming Lei , Ingo Molnar , Peter Zijlstra , Juri Lelli , Luiz Capitulino Subject: Re: [PATCH] sched/isolation: Allow "isolcpus=" to skip unknown sub-parameters In-Reply-To: <20200214194008.GA1193332@xz-x1> References: <20200204161639.267026-1-peterx@redhat.com> <20200214194008.GA1193332@xz-x1> Date: Fri, 14 Feb 2020 21:28:25 +0100 Message-ID: <877e0oud5i.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Peter Xu writes: > On Tue, Feb 04, 2020 at 11:16:39AM -0500, Peter Xu wrote: >> The "isolcpus=" parameter allows sub-parameters to exist before the >> cpulist is specified, and if it sees unknown sub-parameters the whole >> parameter will be ignored. This design is incompatible with itself >> when we add more sub-parameters to "isolcpus=", because the old >> kernels will not recognize the new "isolcpus=" sub-parameters, then it >> will invalidate the whole parameter so the CPU isolation will not >> really take effect if we start to use the new sub-parameters while >> later we reboot into an old kernel. Instead we will see this when >> booting the old kernel: >> >> isolcpus: Error, unknown flag >> >> The better and compatible way is to allow "isolcpus=" to skip unknown >> sub-parameters, so that even if we add new sub-parameters to it the >> old kernel will still be able to behave as usual even if with the new >> sub-parameter is specified. >> >> Ideally this patch should be there when we introduce the first >> sub-parameter for "isolcpus=", so it's already a bit late. However >> late is better than nothing. > > Ping - Hi, Thomas, do you have any further comment on this patch? Fine with me. Reviewed-by: Thomas Gleixner