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

[Boris Ostrovsky <boris.ostrovsky@amd.com>]

On 01/18/2013 02:00 PM, Konrad Rzeszutek Wilk wrote:
>
> Right, that information is gathered from the MSRs. I think the Xen would
> need to do this since it can do the MSRs correctly and modify the P-states.
>
> So something like this in the hypervisor maybe (not even tested):

Is there any harm in allowing dom0 read P-state registers?

Something along these lines:

diff -r 40881d58e991 xen/arch/x86/traps.c
--- a/xen/arch/x86/traps.c	Thu Jan 17 14:47:04 2013 -0500
+++ b/xen/arch/x86/traps.c	Fri Jan 18 09:32:51 2013 -0500
@@ -2535,7 +2535,7 @@ static int emulate_privileged_op(struct
          case MSR_K8_PSTATE7:
              if ( boot_cpu_data.x86_vendor != X86_VENDOR_AMD )
                  goto fail;
-            if ( !is_cpufreq_controller(v->domain) )
+            if ( d->domain_id != 0 )
              {
                  regs->eax = regs->edx = 0;
                  break;


(It does seem to fix the bug too)

-boris


>
> diff --git a/xen/arch/x86/acpi/cpufreq/powernow.c b/xen/arch/x86/acpi/cpufreq/powernow.c
> index a9b7792..54e7808 100644
> --- a/xen/arch/x86/acpi/cpufreq/powernow.c
> +++ b/xen/arch/x86/acpi/cpufreq/powernow.c
> @@ -146,7 +146,40 @@ static int powernow_cpufreq_target(struct cpufreq_policy *policy,
>
>       return 0;
>   }
> +#define MSR_AMD_PSTATE_DEF_BASE     0xc0010064
> +static void amd_fixup_frequency(struct xen_processor_px *px, int i)
> +{
> +	u32 hi, lo, fid, did;
> +	int index = px->control & 0x00000007;
> +
> +	if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD)
> +		return;
> +
> +	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 & 0x80000000))
> +            return;
> +
> +		fid = lo & 0x3f;
> +		did = (lo >> 6) & 7;
> +		if (boot_cpu_data.x86 == 0x10)
> +			px->core_frequency = (100 * (fid + 0x10)) >> did;
> +		else
> +			px->core_frequency = (100 * (fid + 8)) >> did;
> +	}
> +}
> +
> +static void amd_fixup_freq(struct processor_performance *perf)
> +{
>
> +    int i;
> +
> +    for (i = 0; i < perf->state_count; i++)
> +        amd_fixup_frequency(perf->states, i);
> +
> +}
>   static int powernow_cpufreq_verify(struct cpufreq_policy *policy)
>   {
>       struct acpi_cpufreq_data *data;
> @@ -158,6 +191,8 @@ static int powernow_cpufreq_verify(struct cpufreq_policy *policy)
>
>       perf = &processor_pminfo[policy->cpu]->perf;
>
> +    amd_fixup_freq(perf);
> +
>       cpufreq_verify_within_limits(policy, 0,
>           perf->states[perf->platform_limit].core_frequency * 1000);
>
>
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