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SubjectRe: [PATCH 1/2] perf/x86/rapl: Add support for Intel Meteor Lake
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On 1/6/23 06:38, Zhang, Rui wrote:
> My original proposal is that, instead of maintaining model lists in a
> series of different drivers, can we use feature flags instead, and
> maintain them in a central place instead of different drivers. say,
> something like
>
> static const struct x86_cpu_id intel_pm_features[] __initconst = {
> X86_MATCH_INTEL_FAM6_MODEL(SKYLAKE_L, X86_FEATURE_RAPL | X86_FEATURE_TCC_COOLING),
> X86_MATCH_INTEL_FAM6_MODEL(SKYLAKE_X, X86_FEATURE_RAPL | X86_FEATURE_UNCORE_FREQ),
> ...
> X86_MATCH_INTEL_FAM6_MODEL(ALDERLAKE, X86_FEATURE_RAPL | X86_FEATURE_TCC_COOLING),
> X86_MATCH_INTEL_FAM6_MODEL(SAPPHIRERAPIDS_X, X86_FEATURE_RAPL | X86_FEATURE_UNCORE_FREQ),
> ...
> {},
> };
> And then set the feature flags based on this, and make the drivers test
> the feature flags.

That works if you have very few features. SKYLAKE_X looks to have on
the order of 15 model-specific features, or at least references in the code.

That means that the

X86_MATCH_INTEL_FAM6_MODEL(SKYLAKE_X, ...

list goes on for 15 features. It's even worse than that because you'd
*like* to be able to scan up and down the list looking for, say, "all
the CPUs that support RAPL". But, if you do that, you actually need a
table -- a really wide table -- for *all* the features and a column for
each.

What we have now isn't bad. The only real way to fix this is to have
the features enumerated *properly*, aka. architecturally.

I get it, Intel doesn't want to dedicate CPUID bits and architecture to
one-offs. But, at the point that there are a dozen CPU models across
three or four different CPU generations, it's time to revisit it. Could
you help our colleagues revisit it, please?

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