Re: [PATCH v5 2/6] perf arm64: Allow version comparisons of CPU IDs

[James Clark]

On 14/08/2023 15:43, John Garry wrote:
> On 14/08/2023 15:15, James Clark wrote:
>>
>> On 14/08/2023 14:07, John Garry wrote:
>>> On 11/08/2023 15:39, James Clark wrote:
>>>> Currently variant and revision fields are masked out of the MIDR so
>>>> it's not possible to compare different versions of the same CPU.
>>>> In a later commit a workaround will be removed just for N2 r0p3, so
>>>> enable comparisons on version.
>>>>
>>>> This has the side effect of changing the MIDR stored in the header of
>>>> the perf.data file to no longer have masked version fields.
>>> Did you consider adding a raw version of _get_cpuid(), which returns the
>>> full MIDR just for the purpose of caller strcmp_cpuid_str()?
>> I did, but I thought that seeing as it would only be used in one place,
>> and that changing the existing one didn't break anything, that it was
>> better to not fragment the CPU ID interface. I thought it might also
>> have repercussions for the other architectures as well. It would also
>> mean that the MIDR that's stored in the header wouldn't have the version
>> information, which if we're starting to do things with that could be bad.
>>
>> There are already callers of strcmp_cpuid_str() so it's probably best to
>> keep it using the same get_cpuid() string. Unless there is a reason
>> _not_  to do it? There isn't really anything that can't be done with it
>> accepting/returning the full unmasked MIDR. If you want the old
>> behavior, you just set the version fields to 0, which I've also used in
>> a later patch and is already done in mapfile.csv
>>
> 
> ok, fine, so we seems that we would be following x86 on this in terms of
> using strcmp_cpuid_str(). It would be good to mention that there is
> already a weak version of strcmp_cpuid_str() for !x86 in your commit
> message.
> 

Yep I can add this.

> Let me check your code again...
> 
> Thanks,
> John