Re: [PATCH 0/3] x86: Add initial support to discover Intel hybrid CPUs

[Thomas Gleixner <tglx@linutronix.de>]

On Fri, Oct 02 2020 at 19:17, Tony Luck wrote:

> On Sat, Oct 03, 2020 at 03:39:29AM +0200, Thomas Gleixner wrote:
>> On Fri, Oct 02 2020 at 13:19, Ricardo Neri wrote:
>> > Add support to discover and enumerate CPUs in Intel hybrid parts. A hybrid
>> > part has CPUs with more than one type of micro-architecture. Thus, certain
>> > features may only be present in a specific CPU type.
>> >
>> > It is useful to know the type of CPUs present in a system. For instance,
>> > perf may need to handle CPUs differently depending on the type of micro-
>> > architecture. Decoding machine check error logs may need the additional
>> > micro-architecture type information, so include that in the log.
>> 
>> 'It is useful' as justification just makes me barf.
>
> This isn't "hetero" ... all of the cores are architecturally the same.

The above clearly says:

>> > A hybrid part has CPUs with more than one type of micro-architecture.

Can you folks talk to each other and chose non-ambigous wording in
changelogs and cover letters?

> If CPUID says that some feature is supported, then it will be supported
> on all of the cores.

That's a different story.

> There might be some model specific performance counter events that only
> apply to some cores. Or a machine check error code that is logged in the
> model specific MSCOD field of IA32_MCi_STATUS. But any and all code can run
> on any core.

Ok. The perf side should be doable, IIRC we already have something like
that, but Peter should know better.

> Sure there will be some different power/performance tradeoffs on some
> cores. But we already have that with some cores able to achieve higher
> turbo frequencies than others.

Right, that's not a problem.

Thanks,

        tglx