Re: [PATCH -v2] x86, tsc: Limit CPU frequency calibration on AMD

[Borislav Petkov <bp@amd64.org>]

From: "H. Peter Anvin" <hpa@zytor.com>
Date: Tue, Aug 24, 2010 at 06:33:07PM -0400

> Build failure:
> 
> /home/hpa/kernel/linux-2.6-tip.cpu/arch/x86/kernel/cpu/amd.c: In
> function ‘amd_calibrate_cpu’:
> /home/hpa/kernel/linux-2.6-tip.cpu/arch/x86/kernel/cpu/amd.c:397: error:
> implicit declaration of function ‘avail_to_resrv_perfctr_nmi_bit’
> /home/hpa/kernel/linux-2.6-tip.cpu/arch/x86/kernel/cpu/amd.c:409: error:
> implicit declaration of function ‘reserve_perfctr_nmi’
> /home/hpa/kernel/linux-2.6-tip.cpu/arch/x86/kernel/cpu/amd.c:410: error:
> implicit declaration of function ‘reserve_evntsel_nmi’
> /home/hpa/kernel/linux-2.6-tip.cpu/arch/x86/kernel/cpu/amd.c:429: error:
> implicit declaration of function ‘release_perfctr_nmi’
> /home/hpa/kernel/linux-2.6-tip.cpu/arch/x86/kernel/cpu/amd.c:430: error:
> implicit declaration of function ‘release_evntsel_nmi’
> 
> Reproducible by doing "make ARCH=i386 allnoconfig".

Sh*t, I can't catch a break with that Kconfig dependency stuff, can I?

This happens because perfctr-watchdog.c gets pulled in by
CONFIG_X86_LOCAL_APIC which is, _of course_, not selected in an
allnoconfig build. Fixing this would mean exporting all that perfcounter
reservation functionality for the allnoconfig case, which is of course
doable but I'm starting to question the need for recalibrating the TSC
at all:

I mean, in the 99% of the cases MSRC001_0015[24] should be set by the
BIOS and if not then the BIOS which does that is pretty b0rked anyway.
So I'm thinking of removing the recalibration code and simply warning
the user instead, for the 1% case.

Andreas, what do you think?

-- 
Regards/Gruss,
Boris.

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