Messages in this thread | | | Date | Wed, 23 Apr 2014 16:49:55 +0200 | Subject | Re: [PATCH] perf/x86/intel: Use rdmsrl_safe when initializing RAPL PMU. | From | Stephane Eranian <> |
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On Wed, Apr 23, 2014 at 4:45 PM, Peter Zijlstra <peterz@infradead.org> wrote: > On Wed, Apr 23, 2014 at 04:31:32PM +0200, Stephane Eranian wrote: >> 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. > > Weird; so the way it works is that it adds an exception table entry for > the wrmsr instruction, so when the wrmsr generates a fault due to being > an invalid msr the fault handler looks at the exception table, and finds > the entry, which instructs it to continue execution at the error path > and return -EFAULT. > On your machine, booted with 3.15-rc2, do you have /sys/devices/power? If not, and you have at least an SNB, you should have RAPL and that RAPL_UNIT MSR.
Proof is that if you read that MSR using /dev/cpu/msr it works just fine: # modprobe msr # rdmsr 0x606 a1003
So something is broken somewhere.
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