Date: Thu, 24 Jan 2013 11:11:01 -0500 From: John Baldwin <jhb@freebsd.org> To: freebsd-hackers@freebsd.org Cc: Sushanth Rai <sushanth_rai@yahoo.com>, mjacob@freebsd.org, Ian Lepore <ian@freebsd.org> Subject: Re: NMI watchdog functionality on Freebsd Message-ID: <201301241111.01629.jhb@freebsd.org> In-Reply-To: <1358960253.32417.467.camel@revolution.hippie.lan> References: <1358894455.17521.YahooMailClassic@web181706.mail.ne1.yahoo.com> <5100142D.7040904@freebsd.org> <1358960253.32417.467.camel@revolution.hippie.lan>
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On Wednesday, January 23, 2013 11:57:33 am Ian Lepore wrote: > On Wed, 2013-01-23 at 08:47 -0800, Matthew Jacob wrote: > > 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). > > > > I think there's value in the NMI watchdog idea, but unless you back it > up with a real hardware watchdog you don't really have full watchdog > functionality. If the NMI can get the OS to produce some extra info, > that's great, and using an NMI gives you a good chance of doing that > even if it is normal interrupt processing that has wedged the machine. > But calling panic() invokes plenty of processing that can get wedged in > other ways, so even an NMI-based watchdog isn't g'teed to get the > machine running again. > > But adding a real hardware watchdog that fires on a slightly longer > timeout than the NMI watchdog gives you the best of everything: you get > information if it's possible to produce it, and you get a real hardware > reset shortly thereafter if producing the info fails. The IPMI watchdog facility has support for a pre-interrupt that fires before the real watchdog. I have coded up support for it in a branch but haven't found any hardware that supports it that I could use to test them. However, you could use an NMI pre-timer via the local APIC timer as a generic pre-timer for other hardware watchdogs. -- John Baldwin
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