Re: kernel 3.7+ cpufreq regression on AMD system running as dom0

Borislav Petkov
2013-01-14T16:34:49Z

On Mon, Jan 14, 2013 at 04:58:54PM +0100, Stefan Bader wrote:
> Starting with kernel v3.7 the following commit added a quirk
> to obtain the real frequencies of certain AMD systems:
>
> commit f594065faf4f9067c2283a34619fc0714e79a98d
> Author: Matthew Garrett <mjg@redhat.com>
> Date: Tue Sep 4 08:28:06 2012 +0000
>
> ACPI: Add fixups for AMD P-state figures
>
> When running bare-metal, on my Opteron 6128 test box results
> in the frequencies remaining effectively unchanged:
> [ 5.475735] P0: MSR(hi,lo): 8000015c-50004004
> [ 5.479049] P0: fid=0x4, did=0x0, freq: 2000 -> 2000
> [ 5.484001] P1: MSR(hi,lo): 8000014c-50004a4e
> [ 5.487314] P1: fid=0xe, did=0x1, freq: 1500 -> 1500
> [ 5.492272] P2: MSR(hi,lo): 80000141-50005048
> [ 5.495584] P2: fid=0x8, did=0x1, freq: 1200 -> 1200
> [ 5.500540] P3: MSR(hi,lo): 80000138-50005844
> [ 5.503853] P3: fid=0x4, did=0x1, freq: 1000 -> 1000
> [ 5.508812] P4: MSR(hi,lo): 80000131-50005c40
> [ 5.512125] P4: fid=0x0, did=0x1, freq: 800 -> 800
>
> However running as dom0 under Xen 4.2, reading this MSR returns
> null:
> [ 11.613068] P0: MSR(hi,lo): 00000000-00000000
> [ 11.613074] P0: fid=0x0, did=0x0, freq: 2000 -> 1600
> [ 11.613078] P1: MSR(hi,lo): 00000000-00000000
> [ 11.613081] P1: fid=0x0, did=0x0, freq: 1500 -> 1600
> [ 11.613085] P2: MSR(hi,lo): 00000000-00000000
> [ 11.613088] P2: fid=0x0, did=0x0, freq: 1200 -> 1600
> [ 11.613091] P3: MSR(hi,lo): 00000000-00000000
> [ 11.613094] P3: fid=0x0, did=0x0, freq: 1000 -> 1600
> [ 11.613098] P4: MSR(hi,lo): 00000000-00000000
> [ 11.613101] P4: fid=0x0, did=0x0, freq: 800 -> 1600
>
> And this results in Xen failing to change the governor:
> "(XEN) Fail change to ondemand governor"
>
> I suppose this ultimately requires some support in the hypervisor
> to pass through the real values. But since this is at least on my
> combination of Xen 4.2 + kernel v3.7+ and AMD family 0x10 CPU a
> regression compared to older kernels, I wonder whether the following
> change might be something that should go into mainline:
>
> --- 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.

> fid = lo & 0x3f;
> did = (lo >> 6) & 7;
> if (boot_cpu_data.x86 == 0x10)
>
> I tested something similar (so hopefully I have not failed on slapping
> together a cleaned up version), which did resolve the problem.
>
> -Stefan
>
> Reference: https://bugs.launchpad.net/bugs/1078619

Adding the new Andre. :-) Andre, what did we do for powernow-k8 on xen
so that the F10h 50MHz steps quirk would work?

Thanks.

--
Regards/Gruss,
Boris.

Sent from a fat crate under my desk. Formatting is fine.
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