Re: [PATCH] x86: retrieve and log CPU frequency information

[Jan Beulich <jbeulich@xxxxxxxx>]

On 14.05.2020 17:32, Roger Pau Monné wrote:
> On Thu, May 14, 2020 at 03:38:18PM +0200, Jan Beulich wrote:
>> On 14.05.2020 15:10, Roger Pau Monné wrote:
>>> On Wed, Apr 15, 2020 at 01:55:24PM +0200, Jan Beulich wrote:
>>>> While from just a single Skylake system it is already clear that we
>>>> can't base any of our logic on CPUID leaf 15 [1] (leaf 16 is
>>>> documented to be used for display purposes only anyway), logging this
>>>> information may still give us some reference in case of problems as well
>>>> as for future work. Additionally on the AMD side it is unclear whether
>>>> the deviation between reported and measured frequencies is because of us
>>>> not doing well, or because of nominal and actual frequencies being quite
>>>> far apart.
>>>
>>> Can you add some reference to the AMD implementation? I've looked at
>>> the PMs and haven't been able to find a description of some of the
>>> MSRs, like 0xC0010064.
>>
>> Take a look at
>>
>> https://developer.amd.com/resources/developer-guides-manuals/
>>
>> I'm unconvinced a reference needs adding here.
> 
> Do you think it would be sensible to introduce some defines for at
> least 0xC0010064? (ie: MSR_AMD_PSTATE_DEF_BASE)
> 
> I think it would make it easier to find on the manuals.

I did consider doing so at the time, but dropped the idea as we have
a few more examples where we use bare MSR numbers when they're used
just once or very rarely. What I'm not sure about is whether the
name would help finding the doc - the doc is organized by MSR number
after all.

Jan