From owner-freebsd-hackers@FreeBSD.ORG  Wed Jan 23 16:47:52 2013
Return-Path: <owner-freebsd-hackers@FreeBSD.ORG>
Delivered-To: freebsd-hackers@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 by hub.freebsd.org (Postfix) with ESMTP id B6AEF6A5
 for <freebsd-hackers@freebsd.org>; Wed, 23 Jan 2013 16:47:52 +0000 (UTC)
 (envelope-from mjacob@freebsd.org)
Received: from ns1.feral.com (ns1.feral.com [192.67.166.1])
 by mx1.freebsd.org (Postfix) with ESMTP id 764AF75
 for <freebsd-hackers@freebsd.org>; Wed, 23 Jan 2013 16:47:52 +0000 (UTC)
Received: from [192.168.135.7] (quaver.net [76.14.49.207])
 (authenticated bits=0)
 by ns1.feral.com (8.14.5/8.14.4) with ESMTP id r0NGlkJR032793
 (version=TLSv1/SSLv3 cipher=DHE-RSA-CAMELLIA256-SHA bits=256 verify=NO)
 for <freebsd-hackers@freebsd.org>; Wed, 23 Jan 2013 08:47:46 -0800 (PST)
 (envelope-from mjacob@freebsd.org)
Message-ID: <5100142D.7040904@freebsd.org>
Date: Wed, 23 Jan 2013 08:47:41 -0800
From: Matthew Jacob <mjacob@freebsd.org>
Organization: FreeBSD
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64;
 rv:17.0) Gecko/20130107 Thunderbird/17.0.2
MIME-Version: 1.0
To: freebsd-hackers@freebsd.org
Subject: Re: NMI watchdog functionality on Freebsd
References: <1358894455.17521.YahooMailClassic@web181706.mail.ne1.yahoo.com>
 <201301231025.41118.jhb@freebsd.org>
In-Reply-To: <201301231025.41118.jhb@freebsd.org>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.2.7
 (ns1.feral.com [192.67.166.1]); Wed, 23 Jan 2013 08:47:46 -0800 (PST)
X-BeenThere: freebsd-hackers@freebsd.org
X-Mailman-Version: 2.1.14
Precedence: list
Reply-To: mjacob@freebsd.org
List-Id: Technical Discussions relating to FreeBSD
 <freebsd-hackers.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/options/freebsd-hackers>, 
 <mailto:freebsd-hackers-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-hackers>
List-Post: <mailto:freebsd-hackers@freebsd.org>
List-Help: <mailto:freebsd-hackers-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>,
 <mailto:freebsd-hackers-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Wed, 23 Jan 2013 16:47:52 -0000

On 1/23/2013 7:25 AM, John Baldwin wrote:
> On Tuesday, January 22, 2013 5:40:55 pm Sushanth Rai wrote:
>> Hi,
>>
>> Does freebsd have some functionality similar to  Linux's NMI watchdog ? I'm
> aware of ichwd driver, but that depends to WDT to be available in the
> hardware. Even when it is available, BIOS needs to support a mechanism to
> trigger a OS level recovery to get any useful information when system is
> really wedged (with interrupt disabled)
The principle purpose of a watchdog is to keep the system from hanging. 
Information is secondary. The ichwd driver can use the LPC part of ICH 
hardware that's been there since ICH version 4. I implemented this more 
fully at Panasas. The first importance is to keep the system from being 
hung. The next piece of information is to detect, on reboot, that a 
watchdog event occurred. Finally, trying to isolate why is good.

This is equivalent to the tco_WDT stuff on Linux. It's not interrupt 
driven (it drives the reset line on the processor).