From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754610Ab3BFNRF (ORCPT ); Wed, 6 Feb 2013 08:17:05 -0500 Received: from mail-ee0-f45.google.com ([74.125.83.45]:61605 "EHLO mail-ee0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754132Ab3BFNRA (ORCPT ); Wed, 6 Feb 2013 08:17:00 -0500 Date: Wed, 6 Feb 2013 14:16:55 +0100 From: Ingo Molnar To: Yinghai Lu Cc: Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , linux-kernel@vger.kernel.org, Stoney Wang , stable@kernel.org Subject: Re: [PATCH] x86, apic: Check fadt x2apic phys in x2apic_phys_probe() Message-ID: <20130206131655.GH8696@gmail.com> References: <20130204110304.GD24173@gmail.com> <1360009767-3633-1-git-send-email-yinghai@kernel.org> <20130205122432.GE21455@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Yinghai Lu wrote: > On Tue, Feb 5, 2013 at 4:24 AM, Ingo Molnar wrote: > > > > * Yinghai Lu wrote: > > > >> From: Stoney Wang > >> > >> When HP ProLiant DL980 G7 Server boot without x2apic_phys, there will be > >> intermittent lost interrupts and could result in a hang or data loss. > > > > What does 'boot without x2apic_phys' mean? > > > > Does it mean x2apic_phys=0 boot command line? Or, because > > x2apic_phys is off by default, does it simply mean that if it's > > booted with a default kernel, without any workaround specified > > on the boot command line? > > means that user does not append "x2apic_phys" in boot command line. The user does not append a whole lot of other behavior-modification command line options either! There's no apic=0 line either. Nor smp=0. Adding this essentially irrelevant piece of information to the *FIRST*, most important sentence of the changelog is thus not just confusing but utterly misleading. Communications 101. Instead it should say something like: When a HP ProLiant DL980 G7 Server boots a regular kernel, there will be intermittent lost interrupts which could result in a hang or (in extreme cases) data loss. The reason is that this system only supports x2apic physical mode, while the kernel boots with a logical-cluster default setting. This bug can be worked around by specifying the x2apic_phys=1 boot option, but we want to handle this sytem without requiring manual workarounds. Right? Writing a clean changelog is like writing clean code - you have to learn it if you want to contribute to the kernel smoothly. Think of it as an engineering task: the other required half of modifying kernel code. Thanks, Ingo