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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 60025C35247 for ; Mon, 3 Feb 2020 23:57:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 24A79206B8 for ; Mon, 3 Feb 2020 23:57:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="duCawprx" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727015AbgBCX5u (ORCPT ); Mon, 3 Feb 2020 18:57:50 -0500 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:42109 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726834AbgBCX5u (ORCPT ); Mon, 3 Feb 2020 18:57:50 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1580774268; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=377KzugWtdEB1RiDk7iefCk+Qa+LIHv5m9/4EkwomLQ=; b=duCawprxM30AbMNVHZ3Sx1vZJyJJ+aoQ7bHmnPL65879k2j33FdHFEy7XJVwkLsw1dRBkx EuEO3XXbE28ObsdxoSn/d7qYDvvTkuKBQZL9OspbNdgXkI0PLNfE3HkXv+6GgzRMjRc7pM iW6E+4juy+XQzNq5afP8hokRmiq4hKE= Received: from mail-qv1-f72.google.com (mail-qv1-f72.google.com [209.85.219.72]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-385-ehzYx0NTPqOsuzfdw4nB7A-1; Mon, 03 Feb 2020 18:57:46 -0500 X-MC-Unique: ehzYx0NTPqOsuzfdw4nB7A-1 Received: by mail-qv1-f72.google.com with SMTP id v3so10621112qvm.2 for ; Mon, 03 Feb 2020 15:57:46 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=377KzugWtdEB1RiDk7iefCk+Qa+LIHv5m9/4EkwomLQ=; b=GtoxdrIDvYWEQBLwfN5FTxoiBvMsXKnsjdsJK74lVGUaoNEx7jZ+oj6ypYdu7HT2lL XM6W1YbUVB/uih/BVoNl9K9NNQa8uiTrbPsbExc2zcCDaZCVZktGC15XtjtJoPmyxzGW NqB/hCYDD3BX4BJqwIhZbo6uVTgXDPx/+iMLFU35DrX7ibA8onJHP175PisLftO0/kcd xecPbBeB0Jo+OKd1FWbxFxq6ikIn8LS5wbCUzxBvRtSngTstjjkkK8mffIQbLFsbql3q glYlqLDd2nYRPlV9N2HyTvPaClhWgSkLFE62H4qSlLiDI67QyF4h8pto5JM63jynzPbO rwPw== X-Gm-Message-State: APjAAAVw+UfG+1mAwU3iO4JJWALdm5OMS4OB0Ou/ikHeeGxxEzL862II gWRY/jEQxSt9wnN0I/4+SCQ7LVLLBBsn6masU3Snf3YYF5QQoKe7wnjuJFPvO+VLwIg+gZfg9oG FWJW3I6lMsBU5tRrwIP/TET+t X-Received: by 2002:a05:6214:4f2:: with SMTP id cl18mr25491054qvb.89.1580774266436; Mon, 03 Feb 2020 15:57:46 -0800 (PST) X-Google-Smtp-Source: APXvYqy6N76q16RG6gaA3Ccei9IOEfvL+VW0BlpNSl5MYgnCZ7NxgKf3lkrSb8R3wf0XT5Uq1MHCGA== X-Received: by 2002:a05:6214:4f2:: with SMTP id cl18mr25491037qvb.89.1580774266111; Mon, 03 Feb 2020 15:57:46 -0800 (PST) Received: from xz-x1 ([2607:9880:19c8:32::2]) by smtp.gmail.com with ESMTPSA id 13sm10092406qke.85.2020.02.03.15.57.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 03 Feb 2020 15:57:45 -0800 (PST) Date: Mon, 3 Feb 2020 18:57:43 -0500 From: Peter Xu To: Thomas Gleixner 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 Message-ID: <20200203235743.GH155875@xz-x1> References: <20200120091625.17912-1-ming.lei@redhat.com> <87eevrei7h.fsf@nanos.tec.linutronix.de> <20200203192154.GG155875@xz-x1> <87a75zz2hl.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <87a75zz2hl.fsf@nanos.tec.linutronix.de> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 03, 2020 at 11:15:50PM +0000, Thomas Gleixner wrote: > 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. Hi, Thomas, Just to make sure I understand it right: are you suggesting that we fix up housekeeping_isolcpus_setup() to be able to skip unknown sub parameters? Thanks, -- Peter Xu