[coreboot] [PATCH] Halt TCO timer on Intel 3100 chipset

Carl-Daniel Hailfinger c-d.hailfinger.devel.2006 at gmx.net
Sat Apr 19 04:16:56 CEST 2008

On 18.04.2008 17:46, ron minnich wrote:
> Stuff Learned The Hard Way: experience I have had with fallback/normal
> and timers suggests this:
> bios should set the watchdog timer, very early, to fire in, say, 5 minutes
> the final payload (linux) should clear the timer, but not until it
> hits a runlevel such that it is network reachable (and hence
> manageable), and then, the remote network manager system initiates the
> watchdog reset. The decision should not be made locally.
> So, you have to look at the system -- at what point is the system
> reachable from remote?
> - not when the bios tries to boot a payload (could be a bug in bios
> that breaks payload)
> - not when payload tries to boot os (ditto)
> - not when os is booting (ditto)
> - not when os is in /etc/rc or equivalent
> but only when os is "up", and presumed working. In fact, the best way
> to reset the watchdog? From remote:
> ssh node watchdog-reset
> Why is this? because the bios, payload, and kernel, and kernel
> runtime, have to be taken as a whole. The system is not really
> considered viable until it's totally booted. The kernel might be on
> flash, and you might have just tweaked it, and broken it -- which I
> have done, on 1024 machines, and thanked my lucky stars for fallback!
> if you can't do "reset the watchdog" from a remote node, over the
> network,  the node is not up in any useful sense. Let it crash into
> fallback.

Good writeup geared at the multiple servers scenario. Putting it in the
wiki under a page called "Watchdog" would be great.

> Obviously this logic does not apply to standalone nodes :-) (well,not
> completely: for standalone, don't clear the timer until you hit
> runlevel 3 or equivalant)

I beg to differ. What happens if the user wants to run an OS which will
not reset the timer? Think Windows, think installation/live CD.

We already have USE_WATCHDOG_ON_BOOT in v2 and we could use that config
var in v3.


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