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

[Alexander Shishkin]

Andi Kleen <andi@xxxxxxxxxxxxxx> writes:

> Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx> 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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