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

[Andreas Herrmann]

On Wed, Aug 25, 2010 at 03:04:54PM +0200, Andreas Herrmann wrote:
> On Wed, Aug 25, 2010 at 03:06:53AM -0400, Borislav Petkov wrote:
> > From: "H. Peter Anvin" <hpa@xxxxxxxxx>
> > 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 âamd_calibrate_cpuâ:
> > > /home/hpa/kernel/linux-2.6-tip.cpu/arch/x86/kernel/cpu/amd.c:397: error:
> > > implicit declaration of function âavail_to_resrv_perfctr_nmi_bitâ
> > > /home/hpa/kernel/linux-2.6-tip.cpu/arch/x86/kernel/cpu/amd.c:409: error:
> > > implicit declaration of function âreserve_perfctr_nmiâ
> > > /home/hpa/kernel/linux-2.6-tip.cpu/arch/x86/kernel/cpu/amd.c:410: error:
> > > implicit declaration of function âreserve_evntsel_nmiâ
> > > /home/hpa/kernel/linux-2.6-tip.cpu/arch/x86/kernel/cpu/amd.c:429: error:
> > > implicit declaration of function ârelease_perfctr_nmiâ
> > > /home/hpa/kernel/linux-2.6-tip.cpu/arch/x86/kernel/cpu/amd.c:430: error:
> > > implicit declaration of function ârelease_evntsel_nmiâ
> > > 
> > > 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).

... and checking the HWCR MSR and issuing the firmware warning should
only happen if not running on a hypervisor. (Validate whether CPU has
X86_FEATURE_HYPERVISOR bit set or not.)


Andreas

-- 
Operating | Advanced Micro Devices GmbH
  System  | Einsteinring 24, 85609 Dornach b. MÃnchen, Germany
 Research | GeschÃftsfÃhrer: Alberto Bozzo, Andrew Bowd
  Center  | Sitz: Dornach, Gemeinde Aschheim, Landkreis MÃnchen
  (OSRC)  | Registergericht MÃnchen, HRB Nr. 43632


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/