From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S272365AbTGaFo6 (ORCPT ); Thu, 31 Jul 2003 01:44:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S272368AbTGaFo6 (ORCPT ); Thu, 31 Jul 2003 01:44:58 -0400 Received: from twilight.cs.hut.fi ([130.233.40.5]:10877 "EHLO twilight.cs.hut.fi") by vger.kernel.org with ESMTP id S272365AbTGaFo4 (ORCPT ); Thu, 31 Jul 2003 01:44:56 -0400 Date: Thu, 31 Jul 2003 08:44:48 +0300 From: Ville Herva To: Mikael Pettersson Cc: ak@suse.de, linux-kernel@vger.kernel.org Subject: Re: [PATCH] NMI watchdog documentation Message-ID: <20030731054448.GU83336@niksula.cs.hut.fi> Mail-Followup-To: Ville Herva , Mikael Pettersson , ak@suse.de, linux-kernel@vger.kernel.org References: <200307302253.h6UMr0XW024175@harpo.it.uu.se> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200307302253.h6UMr0XW024175@harpo.it.uu.se> User-Agent: Mutt/1.4i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 31, 2003 at 12:53:00AM +0200, you [Mikael Pettersson] wrote: > On Wed, 30 Jul 2003 22:40:52 +0300, Ville Herva wrote: > >Ok, you got me confused (thankfully I didn't submit anything for inclusion > >yet. :) > ... > >So... Should it be something like: > > > >+For x86-64, the needed APIC is always compiled in, and the NMI watchdog is > >+always enabled with perctr mode. Currently, mode=2 (local APIC) does not > > always enabled with I/O-APIC mode. > > >+work on x86-64. IO APIC mode (mode=1) is the default. Using NMI watchdog > > Using local APIC > > >+(mode=1) needs the first performance register, so you can't use it for > > (mode=2) > > >+other purposes (such as high precision performance profiling.) > > >(Is the last sentence only valid for x86-64?) > > No, it's true for both x86 and x86-64. However, both oprofile > and the perfctr driver disable the local APIC NMI watchdog, so > the statement is only true for other drivers that don't do this. Uuh, sorry. Is the one below ok by you for submission to Linus and Marcelo? -- v -- v@iki.fi --- linux/Documentation/nmi_watchdog.txt Sun Jul 27 19:58:26 2003 +++ linux~/Documentation/nmi_watchdog.txt Tue Jul 29 21:08:01 2003 @@ -1,9 +1,11 @@ -Is your ix86 system locking up unpredictably? No keyboard activity, just +[NMI watchdog is available for x86 and x86-64 architectures] + +Is your system locking up unpredictably? No keyboard activity, just a frustrating complete hard lockup? Do you want to help us debugging such lockups? If all yes then this document is definitely for you. -On Intel and similar ix86 type hardware there is a feature that enables +On many x86/x86-64 type hardware there is a feature that enables us to generate 'watchdog NMI interrupts'. (NMI: Non Maskable Interrupt which get executed even if the system is otherwise locked up hard). This can be used to debug hard kernel lockups. By executing periodic @@ -20,6 +22,15 @@ kernel debugging options, such as Kernel Stack Meter or Kernel Tracer, may implicitly disable the NMI watchdog.] +For x86-64, the needed APIC is always compiled in, and the NMI watchdog is +always enabled with I/O-APIC mode (nmi_watchdog=1). Currently, local APIC +mode (nmi_watchdog=2) does not work on x86-64. + +Using local APIC (nmi_watchdog=2) needs the first performance register, so +you can't use it for other purposes (such as high precision performance +profiling.) However, at least oprofile and the perfctr driver disable the +local APIC NMI watchdog automatically. + To actually enable the NMI watchdog, use the 'nmi_watchdog=N' boot parameter. Eg. the relevant lilo.conf entry: