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SubjectRe: [patch] enabling APIC and NMI watchdog on UP systems
On Thu, 28 Sep 2000, Ingo Molnar wrote:

> the attached patch (against test9-pre7) is a cleaned up version Keir
> Fraser's APIC-on-UP patch, and adds the enabling code of Keith Owens which
> programs P6 performance counter 0 as an NMI. (i simplified the code alot -
> there is no problem at all with getting NMIs from two sources, and it's
> not necessary to make it configurable.)
> i'd like to hear about how this patch works for people - it works here on
> SMP systems and on P6 systems. The watchdog is enabled unconditionally -
> this should significantly help debugging lockups on UP systems as well!
> (thanks Keir and Keith!)
> Ingo

I can't test it right now, but I had a question or two ...

Is it really necessary to use one of the event counters ? this means those
of us using event counters from modules can't use this oopser at
the same time, which is a pity.

Can you not set up the actual APIC timer on a local APIC to deliver NMIs
? (Sorry, been a while since I read the intel docs)

Vincent Oberle has an apic timer module which uses these (link from for anyone interested).

On the other hand it's good to see that us module event counter users
don't have to do that ugly fixmap thing to get back real access to the
local APIC, now that the zero-page thing is gone :)


"The words CON and NUL
Are reserved by the system.
Don't ask; they just are."

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