From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S967416Ab3DROx5 (ORCPT ); Thu, 18 Apr 2013 10:53:57 -0400 Received: from mail.active-venture.com ([67.228.131.205]:58673 "EHLO mail.active-venture.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S967009Ab3DROxz (ORCPT ); Thu, 18 Apr 2013 10:53:55 -0400 X-Originating-IP: 108.223.40.66 Date: Thu, 18 Apr 2013 07:54:13 -0700 From: Guenter Roeck To: Don Zickus Cc: "Eric W. Biederman" , linux-watchdog@vger.kernel.org, kexec@lists.infradead.org, wim@iguana.be, LKML , vgoyal@redhat.com, dyoung@redhat.com Subject: Re: [PATCH v3] watchdog: Add hook for kicking in kdump path Message-ID: <20130418145413.GA1980@roeck-us.net> References: <1366233596-34681-1-git-send-email-dzickus@redhat.com> <87li8gaku0.fsf@xmission.com> <20130418130009.GH79013@redhat.com> <20130418134904.GC2767@roeck-us.net> <20130418135257.GL79013@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130418135257.GL79013@redhat.com> 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 On Thu, Apr 18, 2013 at 09:52:57AM -0400, Don Zickus wrote: > On Thu, Apr 18, 2013 at 06:49:04AM -0700, Guenter Roeck wrote: > > On Thu, Apr 18, 2013 at 09:00:09AM -0400, Don Zickus wrote: > > > On Wed, Apr 17, 2013 at 02:49:59PM -0700, Eric W. Biederman wrote: > > > > Don Zickus writes: > > > > > > > > > A common problem with kdump is that during the boot up of the > > > > > second kernel, the hardware watchdog times out and reboots the > > > > > machine before a vmcore can be captured. > > > > > > > > > > Instead of tellling customers to disable their hardware watchdog > > > > > timers, I hacked up a hook to put in the kdump path that provides > > > > > one last kick before jumping into the second kernel. > > > > > > > > > > The assumption is the watchdog timeout is at least 10-30 seconds > > > > > long, enough to get the second kernel to userspace to kick the watchdog > > > > > again, if needed. > > > > > > > > Why not double the watchdog timeout? and/or pet the watchdog a little > > > > more frequently. > > > > > > I am not sure if the watchdog timeouts can be doubled. I think Guenter > > > was saying some have a max of a couple seconds?? Petting a little more > > > frequently might be an option. Guenter can that be done with a softdog > > > option? > > > > > Most watchdog driver permit at least a minute. Some are more limited. > > Worst I have seen is the BookE watchdog timer (non-Freescale version) > > which has a maximum of three seconds. But that is broken anyway. > > > > Most hardware watchdogs implement a softdog on top of the hardware watchdog > > if the hardware needs to be pinged faster than every 60 seconds. > > > > So, yes, for the most common case you should actually be able to live with a, > > say, 30-60 second timeout which is pinged at least every 5-10 seconds. I thought > > that somehow did not work in your case. Maybe a misunderstanding ? > > No, that will probably work. It is my misunderstanding. Is there a > common way to check the timeout length and the ping frequency? > Usually it is configured in /etc/watchdog.conf if the watchdog package is installed. The standard ping interval is "interval", the timeout is "watchdog-timeout". See "man watchdog.conf" for details. Minimum and maximum values for a given watchdog driver are not exported to user space, so you would have to look into the driver sources to find out what they are. Guenter