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

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Message-ID: <20100825130454.GB4891@loge.amd.com>
Date:	Wed, 25 Aug 2010 15:04:54 +0200
From:	Andreas Herrmann <andreas.herrmann3@....com>
To:	Borislav Petkov <bp@...64.org>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	Alok Kataria <akataria@...are.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>,
	the arch/x86 maintainers <x86@...nel.org>,
	Greg KH <gregkh@...e.de>, "greg@...ah.com" <greg@...ah.com>,
	"ksrinivasan@...ell.com" <ksrinivasan@...ell.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -v2] x86, tsc: Limit CPU frequency calibration on AMD

On Wed, Aug 25, 2010 at 03:06:53AM -0400, Borislav Petkov wrote:
> From: "H. Peter Anvin" <hpa@...or.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?

I opt for removing the recalibration code plus keeping a FIRMWARE_WARN
for borked BIOSes (just in case that there are any old systems with
the wrong setting).


Andreas

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