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 66240C35247 for ; Mon, 3 Feb 2020 23:16:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1134B20721 for ; Mon, 3 Feb 2020 23:16:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727015AbgBCXQD (ORCPT ); Mon, 3 Feb 2020 18:16:03 -0500 Received: from Galois.linutronix.de ([193.142.43.55]:60587 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726331AbgBCXQD (ORCPT ); Mon, 3 Feb 2020 18:16:03 -0500 Received: from tmo-110-211.customers.d1-online.com ([80.187.110.211] 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 1iykwZ-0001eB-Qg; Tue, 04 Feb 2020 00:15:52 +0100 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id 6E26B100720; Mon, 3 Feb 2020 23:15:50 +0000 (GMT) From: Thomas Gleixner To: Peter Xu Cc: Ming Lei , linux-kernel@vger.kernel.org, Ingo Molnar , Peter Zijlstra , Juri Lelli , Luiz Capitulino Subject: Re: [PATCH V4] sched/isolation: isolate from handling managed interrupt In-Reply-To: <20200203192154.GG155875@xz-x1> References: <20200120091625.17912-1-ming.lei@redhat.com> <87eevrei7h.fsf@nanos.tec.linutronix.de> <20200203192154.GG155875@xz-x1> Date: Mon, 03 Feb 2020 23:15:50 +0000 Message-ID: <87a75zz2hl.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: > The new "managed_irq" works for us, thanks for both of your work! > > However I just noticed that this new sub-parameter might break users > if applied incorrectly to old kernels, because iiuc "isolcpus=" > parameter will not apply at all when there's unknown sub-parameters: > > static int __init housekeeping_isolcpus_setup(char *str) > { > unsigned int flags = 0; > > while (isalpha(*str)) { > ... > pr_warn("isolcpus: Error, unknown flag\n"); > return 0; > } > ... > } > > Then the same kernel parameter will break isolcpus= if the user > reboots and switches to an older kernel. > > A solution to this could be that we introduce an isolated parameter > for "managed_irq", then on the old kernels only the new parameter will > be ignored rather than the whole "isolcpus=" parameter, so nothing > will break. > > I'm not sure whether it's already too late for this, or if there's any > better alternative. Just raise this question up to see whether we > still have chance to fix this up. No, really. The basic guarantee is that your new kernel is going to work fine with the previous command line, but making a guarantee that new command line options still work on an old kernel are just creating a horrible mess. So if that command line interface was not designed to handle unknown arguments in the first place, you better fix that. Thanks, tglx