Re: [PATCH] perf/x86/intel: Use rdmsrl_safe when initializing RAPL PMU.

Stephane Eranian
2014-04-23T14:37:38Z

On Thu, Mar 13, 2014 at 8:36 PM, Venkatesh Srinivas
<venkateshs@google.com> wrote:
> CPUs which should support the RAPL counters according to
> Family/Model/Stepping may still issue #GP when attempting to access
> the RAPL MSRs. This may happen when Linux is running under KVM and
> we are passing-through host F/M/S data, for example. Use rdmsrl_safe
> to first access the RAPL_POWER_UNIT MSR; if this fails, do not
> attempt to use this PMU.
>
> Signed-off-by: Venkatesh Srinivas <venkateshs@google.com>
> ---
> arch/x86/kernel/cpu/perf_event_intel_rapl.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/perf_event_intel_rapl.c b/arch/x86/kernel/cpu/perf_event_intel_rapl.c
> index 5ad35ad..95700e5 100644
> --- a/arch/x86/kernel/cpu/perf_event_intel_rapl.c
> +++ b/arch/x86/kernel/cpu/perf_event_intel_rapl.c
> @@ -511,6 +511,7 @@ static int rapl_cpu_prepare(int cpu)
> struct rapl_pmu *pmu = per_cpu(rapl_pmu, cpu);
> int phys_id = topology_physical_package_id(cpu);
> u64 ms;
> + u64 msr_rapl_power_unit_bits;
>
> if (pmu)
> return 0;
> @@ -518,6 +519,9 @@ static int rapl_cpu_prepare(int cpu)
> if (phys_id < 0)
> return -1;
>
> + if (!rdmsrl_safe(MSR_RAPL_POWER_UNIT, &msr_rapl_power_unit_bits))
> + return -1;
> +
I have a problem with this patch on native hardware. This
rdmsrl_safe() systematically
fails when I know the MSR is perfectly valid on the CPU. Consequently, RAPL PMU
is disabled when I tried on IvyBridge and Haswell CPUs.

I don't know the internals of rdmsrl_safe(). Maybe it is invoked too
early in the boot process.

Please fix this.

> pmu = kzalloc_node(sizeof(*pmu), GFP_KERNEL, cpu_to_node(cpu));
> if (!pmu)
> return -1;
> @@ -531,8 +535,7 @@ static int rapl_cpu_prepare(int cpu)
> *
> * we cache in local PMU instance
> */
> - rdmsrl(MSR_RAPL_POWER_UNIT, pmu->hw_unit);
> - pmu->hw_unit = (pmu->hw_unit >> 8) & 0x1FULL;
> + pmu->hw_unit = (msr_rapl_power_unit_bits >> 8) & 0x1FULL;
> pmu->pmu = &rapl_pmu_class;
>
> /*
> @@ -649,7 +652,9 @@ static int __init rapl_pmu_init(void)
> get_online_cpus();
>
> for_each_online_cpu(cpu) {
> - rapl_cpu_prepare(cpu);
> + ret = rapl_cpu_prepare(cpu);
> + if (ret)
> + goto out;
> rapl_cpu_init(cpu);
> }
>
> @@ -672,6 +677,7 @@ static int __init rapl_pmu_init(void)
> hweight32(rapl_cntr_mask),
> ktime_to_ms(pmu->timer_interval));
>
> +out:
> put_online_cpus();
>
> return 0;
> --
> 1.9.0.279.gdc9e3eb
>