linux-kernel - Re: [PATCH 4/6] perf/tool: Parse non-cpu pmu capabilities

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Message-ID: <YmfLU/VMQI0g0Ck0@rric.localdomain>
Date:   Tue, 26 Apr 2022 12:37:07 +0200
From:   Robert Richter <rrichter@....com>
To:     Ravi Bangoria <ravi.bangoria@....com>
CC:     <peterz@...radead.org>, <acme@...nel.org>, <mingo@...hat.com>,
        <mark.rutland@....com>, <jolsa@...nel.org>, <namhyung@...nel.org>,
        <tglx@...utronix.de>, <bp@...en8.de>, <irogers@...gle.com>,
        <yao.jin@...ux.intel.com>, <james.clark@....com>,
        <leo.yan@...aro.org>, <kan.liang@...ux.intel.com>,
        <ak@...ux.intel.com>, <eranian@...gle.com>,
        <like.xu.linux@...il.com>, <x86@...nel.org>,
        <linux-perf-users@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <sandipan.das@....com>, <ananth.narayan@....com>,
        <kim.phillips@....com>, <santosh.shukla@....com>
Subject: Re: [PATCH 4/6] perf/tool: Parse non-cpu pmu capabilities

On 25.04.22 10:13:21, Ravi Bangoria wrote:

> diff --git a/tools/perf/Documentation/perf.data-file-format.txt b/tools/perf/Documentation/perf.data-file-format.txt
> index f56d0e0fbff6..dea3acb36558 100644
> --- a/tools/perf/Documentation/perf.data-file-format.txt
> +++ b/tools/perf/Documentation/perf.data-file-format.txt
> @@ -435,6 +435,24 @@ struct {
>  	} [nr_pmu];
>  };
>  
> +	HEADER_PMU_CAPS = 32,
> +
> +	List of pmu capabilities (except cpu pmu which is already
> +	covered by HEADER_CPU_PMU_CAPS)
> +
> +struct {
> +	u32 nr_pmus;
> +	struct {
> +		u8 core_type;	/* For hybrid topology */
> +		char pmu_name[];
> +		u16 nr_caps;
> +		struct {
> +			char name[];
> +			char value[];
> +		} [nr_caps];
> +	} [nr_pmus];
> +};
> +

This looks quite a bit complex and special.

Why not just reusing struct nr_cpu_pmu_caps (id 28)? Rename it and
introduce macros for backwards compatability if needed.

pmu_name is already encoded in sysfs and core_type could be a caps
value?

-Robert