Re: [Xen-devel] kernel 3.7+ cpufreq regression on AMD system runningas dom0

[Stefan Bader]

On 01/16/2013 11:26 AM, Jan Beulich wrote:
> > > > On 15.01.13 at 18:53, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> wrote:
> > On Mon, Jan 14, 2013 at 05:34:45PM +0100, Borislav Petkov wrote:
> > > On Mon, Jan 14, 2013 at 04:58:54PM +0100, Stefan Bader wrote:
> > > > --- a/drivers/acpi/processor_perflib.c
> > > > +++ b/drivers/acpi/processor_perflib.c
> > > > @@ -340,6 +340,9 @@ static void amd_fixup_frequency(struct acpi_processor_px *px
> > > >          if ((boot_cpu_data.x86 == 0x10 && boot_cpu_data.x86_model < 10)
> > > >              || boot_cpu_data.x86 == 0x11) {
> > > >                  rdmsr(MSR_AMD_PSTATE_DEF_BASE + index, lo, hi);
> > > > +               /* Bit 63 indicates whether contents are valid */
> > > > +               if (!(hi & 0x8000000))
> > > > +                       return;
> > >
> > > I don't think that's the right change - this is fixing baremetal so that
> > > it works on xen. And besides, this code was in powernow-k8 before so I'm
> > > wondering why did it work then.
> >
> > Powernow-k8 only populated the cpufreq policy information. This library
> > (processor_perflib) is the generic library used for ACPI P-states parsing.
> > This specific function (acpi_processor_get_performance_states) is just
> > used to fetch and parse the P-states.
> >
> > Xen-acpi-processor (which we use to upload the P and C-states to the
> > hypervisor) ends up calling this library to parse the P-states
> > and this unfortunate quirk clamps the P-states based on the MSRS.
> >
> > It is odd that this CPU specific quirk got added in this generic
> > library. Is there no ACPI quirk system similar to how DMI quirks
> > are handled?
> >
> > Anyhow, I think this patch makes sense - it makes sure that the
> > MSR value is sane.
> >
> > Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
>
> Did someone actually _test_ that patch? I ask because the mask
> used (0x8000000) doesn't check bit 63 as the comment says, but
> bit 59 instead...
>
> Jan
Not this version which I did at the end of a day to have a cleaned up version to 
discuss. And obviously I managed to get the number of zeros wrong. :(

The comment is right and it should be 0x80000000
--
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/