linux-kernel - Re: [PATCH 03/20] perf/x86/intel: Parse CPUID archPerfmonExt leaves for non-hybrid CPUs

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Message-ID: <Z5KRT-F7MbTs6g6y@tassilo>
Date: Thu, 23 Jan 2025 10:58:23 -0800
From: Andi Kleen <ak@...ux.intel.com>
To: Dapeng Mi <dapeng1.mi@...ux.intel.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Kan Liang <kan.liang@...ux.intel.com>,
	Eranian Stephane <eranian@...gle.com>, linux-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org, Dapeng Mi <dapeng1.mi@...el.com>
Subject: Re: [PATCH 03/20] perf/x86/intel: Parse CPUID archPerfmonExt leaves
 for non-hybrid CPUs

> +	/*
> +	 * The archPerfmonExt (0x23) includes an enhanced enumeration of
> +	 * PMU architectural features with a per-core view. For non-hybrid,
> +	 * each core has the same PMU capabilities. It's good enough to
> +	 * update the x86_pmu from the booting CPU. For hybrid, the x86_pmu
> +	 * is used to keep the common capabilities. Still keep the values
> +	 * from the leaf 0xa. The core specific update will be done later
> +	 * when a new type is online.
> +	 */
> +	if (!is_hybrid() && boot_cpu_has(X86_FEATURE_ARCH_PERFMON_EXT))
> +		update_pmu_cap(NULL);

It seems ugly to have these different code paths. Couldn't non hybrid
use x86_pmu in the same way? I assume it would be a larger patch.

-Andi