Re: [resend] [PATCH] MSR_IA32_PERF_STATUS support

[Alexander Graf <alex-r27SGEef+tmzQB+pC5nmwQ@public.gmane.org>]

Avi Kivity wrote:
> Alexander Graf wrote:
>> This is a resend of a mail I sent on 01/10/2008. I did not receive any
>> response, so I assume it was lost.
>>
>> The patch is really minor, does not break any compatibility (the MSR is
>> Intel family 13+) and makes Darwin work.
>>
>> --- old mail ---
>>
>> This patch adds support for the MSR MSR_IA32_PERF_STATUS. This is
>> required to boot Darwin.
>>
>> I only implemented dummy support, as the real value would be of no
>> meaning to any OS I know so far anyway and is only implemented on very
>> recent Intel CPUs.
>>   
>
> I see some documentation of this in 13.1.1, but is there somewhere
> with more information?
>
The only proper source of information I found was the XNU kernel, which
implements a full interpretation of the MSR values. Basically the high
bits are the CPU multiplier, while the low bits represent the number the
TSC advances in one cycle.

There is also a bit which multiplies everything by 2, but maybe the
Intel people on this list can tell us more about it.


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