Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262873AbUKRSkg (ORCPT ); Thu, 18 Nov 2004 13:40:36 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262861AbUKRSjE (ORCPT ); Thu, 18 Nov 2004 13:39:04 -0500 Received: from pollux.ds.pg.gda.pl ([153.19.208.7]:35076 "EHLO pollux.ds.pg.gda.pl") by vger.kernel.org with ESMTP id S262846AbUKRShM (ORCPT ); Thu, 18 Nov 2004 13:37:12 -0500 Date: Thu, 18 Nov 2004 18:37:07 +0000 (GMT) From: "Maciej W. Rozycki" To: Andrew Morton , Stas Sergeev Cc: Linux kernel Subject: Re: 2.6.10-rc1-mm5 In-Reply-To: <419CDB6F.2090406@aknet.ru> Message-ID: References: <41967669.3070707@aknet.ru> <4198EFE5.5010003@aknet.ru> <419A38EE.8000202@aknet.ru> <419CB75C.3080605@aknet.ru> <419CDB6F.2090406@aknet.ru> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2166 Lines: 48 On Thu, 18 Nov 2004, Stas Sergeev wrote: > Ah, thanks for explanations! > Indeed it works as you say. > Very usefull info, perhaps worth > being added to documentation? > So if you ACK the attached patch, > I ask Andrew to please apply it. Sure, no problem with that. > Andrew, the attached patch adds > the information about the NMI > watchdog frequency caveats to the > Documentation/nmi_watchdog.txt > Unless there are any objections, > please apply. Signed-off-by: Maciej W. Rozycki --- linux/Documentation/nmi_watchdog.txt.old 2004-10-21 21:21:56.000000000 +0400 +++ linux/Documentation/nmi_watchdog.txt 2004-11-18 20:16:37.972370552 +0300 @@ -54,6 +54,20 @@ cannot even accept NMI interrupts, or the crash has made the kernel unable to print messages. +Be aware that when using local APIC, the frequency of NMI interrupts +it generates, depends on the system load. The local APIC NMI watchdog, +lacking a better source, uses the "cycles unhalted" event. As you may +guess it doesn't tick when the CPU is in the halted state (which happens +when the system is idle), but if your system locks up on anything but the +"hlt" processor instruction, the watchdog will trigger very soon as the +"cycles unhalted" event will happen every clock tick. If it locks up on +"hlt", then you are out of luck -- the event will not happen at all and the +watchdog won't trigger. This is a shortcoming of the local APIC watchdog +-- unfortunately there is no "clock ticks" event that would work all the +time. The I/O APIC watchdog is driven externally and has no such shortcoming. +But its NMI frequency is much higher, resulting in a more significant hit +to the overall system performance. + NOTE: starting with 2.4.2-ac18 the NMI-oopser is disabled by default, you have to enable it with a boot time parameter. Prior to 2.4.2-ac18 the NMI-oopser is enabled unconditionally on x86 SMP boxes. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/