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SubjectRe: [patch] enabling APIC and NMI watchdog on UP systems

On Fri, 29 Sep 2000, John Levon wrote:

> 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.

well, you can still use the other event counter. And you can clear the
first counter as well. The Intel performance monitoring utility (perfmon?)
has been using this NMI technique for years, so it's probably the only way
to get periodic NMIs on UP systems, without any extra hardware.

> 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)

unfortunately not. It ignores this setting. I tried it years ago :-)

> 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 zero-page is added if there is no APIC detected, so it's intended
behavior - if there is an APIC in a CPU then we definitely want to enable
it during bootup!

Ingo

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