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Re: [PATCH] perf/x86/intel/pt: Export cpu frequency ratios needed by PT decoders

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Andi Kleen <andi@firstfloor.org> writes:

> Alexander Shishkin <alexander.shishkin@linux.intel.com> writes:
>> +		return sprintf(page, "%lu\n", val);
>> +	case 1:
>> +		cpuid(0x15, &eax, &ebx, &ecx, &edx);
>
> Surely this needs to be protected by a cpuid level check?
> Broadwell for once doesn't have CPUID 0x15.

I couldn't find where this is explicitly said in the SDM. However, the
leaf description says that CPUID.0x15.EBX[31:0]==0 means that the ratio
is not enumerated. I don't see how to better communicate this to
userspace though than to simply have 0 there.

Regards,
--
Alex
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[PATCH] perf/x86/intel/pt: Export cpu frequency ratios needed by PT decoders Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2015-08-27 17:10 +0200
  Re: [PATCH] perf/x86/intel/pt: Export cpu frequency ratios needed by PT decoders Andi Kleen <andi@firstfloor.org> - 2015-08-28 21:40 +0200
    Re: [PATCH] perf/x86/intel/pt: Export cpu frequency ratios needed by PT decoders Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2015-08-31 15:00 +0200
      Re: [PATCH] perf/x86/intel/pt: Export cpu frequency ratios needed by  PT decoders Andi Kleen <andi@firstfloor.org> - 2015-08-31 22:10 +0200

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