RFR: 8268228: TSC is not used for CPUTimeStampCounter on AMD processor [v2]

[Yasumasa Suenaga]

On Fri, 4 Jun 2021 05:08:33 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Yasumasa Suenaga has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fix comments
>
> Hi Yasumasa,
> 
> This seems reasonable to address the observed problem, though I have to wonder why a system with invariant TSC is not properly reporting a maximum frequency? Makes me wonder how many chips may actually be impacted here?
> 
> Thanks,
> David

Thanks @dholmes-ora for your review!
I pushed new commit. Could you review again?

> This seems reasonable to address the observed problem, though I have to wonder why a system with invariant TSC is not properly reporting a maximum frequency?

I guess it is not specified to contain the frequency in brand string, I'm not sure.
In AMD processor, we can seem to get effective frequency from MSR, but it requires kernel mode, so we can't use it.

> Makes me wonder how many chips may actually be impacted here?

I guess AMD processors are affected it at least. For example, Opteron and Athlon do not seem to have its frequency in their brand string.

https://www.cpu-world.com/cgi-bin/CPUID.pl?CPUID=73494
https://www.cpu-world.com/cgi-bin/CPUID.pl?CPUID=74038

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PR: https://git.openjdk.java.net/jdk/pull/4350