Re: [PATCH] 2.4.1-ac1 UP-APIC/NMI watchdog fixes

From: Mikael Pettersson (
Date: Thu Feb 01 2001 - 21:35:37 EST

On Fri, 2 Feb 2001 01:37:28 +0100, Ingo Molnar wrote:

> On Thu, 1 Feb 2001, Mikael Pettersson wrote:
> > This patch (against 2.4.1-ac1) contains the following fixes:
> > * UP-APIC linkage fix: nr_ioapics must be moved from io_apic.c to
> > mpparse.c to permit linking the kernel in pure UP-APIC configs.
> > * NMI watchdog cleanups: mark setup_apic_nmi_watchdog() as __init,
> > fix the K7 init code to not leave any perfctr MSR uninitialised,
> > avoid having to check CPU type in NMI handler.
> > (Yes, the merged wrmsr(,,-1) is safe for P6.)
> thanks Mikael! Did you have a chance to test this on a K7? Does
> UP-APIC-NMI-watchdog code truly 'just work' now on the K7?

I wrote the initial patch using the info I gathered for my
performance-monitoring counters driver. Petr Vandrovec tested
and debugged it. (Alas, I don't yet have a K7 to play with.)

It seems K7 BIOSen keep the local APIC enabled as opposed to
what P6 BIOSen tend to do (at least, Petr's ASUS A7V did),
so in a sense, yes "it just works". The clock denoted by the
event selector is not perfect (it slows down by a factor of
100 when the CPU is idle), but the NMIs do keep coming in.

I might have been able to whip up something better, if AMD
hadn't required an NDA for the K7 BIOS writer's manual. My
regard for them is pretty low right now.

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