linux-kernel - Re: [PATCH v3 2/5] perf header: Parse non-cpu pmu capabilities

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Message-ID: <e578d274-946f-2c73-026d-9b172ce32f19@amd.com>
Date:   Fri, 20 May 2022 09:19:28 +0530
From:   Ravi Bangoria <ravi.bangoria@....com>
To:     Ian Rogers <irogers@...gle.com>
Cc:     acme@...nel.org, peterz@...radead.org, rrichter@....com,
        mingo@...hat.com, mark.rutland@....com, jolsa@...nel.org,
        namhyung@...nel.org, tglx@...utronix.de, bp@...en8.de,
        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, Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [PATCH v3 2/5] perf header: Parse non-cpu pmu capabilities

Hi Ian,

On 20-May-22 3:57 AM, Ian Rogers wrote:
> On Wed, May 18, 2022 at 10:45 PM Ravi Bangoria <ravi.bangoria@....com> wrote:
>>
>> Pmus advertise their capabilities via sysfs attribute files but
>> perf tool currently parses only core(cpu) pmu capabilities. Add
>> support for parsing non-cpu pmu capabilities.
>>
>> Signed-off-by: Ravi Bangoria <ravi.bangoria@....com>
>> ---
>>  .../Documentation/perf.data-file-format.txt   |  18 ++
>>  tools/perf/util/env.c                         |  48 +++++
>>  tools/perf/util/env.h                         |  11 +
>>  tools/perf/util/header.c                      | 198 ++++++++++++++++++
>>  tools/perf/util/header.h                      |   1 +
>>  tools/perf/util/pmu.c                         |  15 +-
>>  tools/perf/util/pmu.h                         |   2 +
>>  7 files changed, 289 insertions(+), 4 deletions(-)
>>
>> diff --git a/tools/perf/Documentation/perf.data-file-format.txt b/tools/perf/Documentation/perf.data-file-format.txt
>> index f56d0e0fbff6..7f8341db9134 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)
> 
> Sorry for the ignorance, is this currently broken for hybrid then?
> Will hybrid have a HEADER_CPU_PMU_CAPS? Presumably this varies between
> ARM's big.little and Alderlake.

It's covered by HEADER_HYBRID_CPU_PMU_CAPS, but that too covers only
cpu pmu. I think I should update the above comment to:

	List of pmu capabilities (except cpu pmu which is already
	covered by HEADER_CPU_PMU_CAPS / HEADER_HYBRID_CPU_PMU_CAPS)

>> +
>> +struct {
>> +       u32 nr_pmus;
>> +       struct {
>> +               u32 core_type;  /* For hybrid topology */
> 
> Could this be pmu_type as presumably we can have capabilities on any
> kind of PMU?

Not sure I follow that question but let me just put my thoughts here.

{core_type, pmu_name} is the unique key here. Considering a hypothetical
scenario: A system has two types of cores P-core and E-core. Certain pmu
inside P-core has some capabilities which are missing in the identical
pmu belonging to E-core. The header will look something like:

struct {
	.nr_pmus = 2,
	[0] = struct {
		.core_type = 0, /* P-core */
		.pmu_name = xyz_pmu,
		.nr_caps = 2,
		[0] = { .name = cap1, .value = value1 },
		[1] = { .name = cap2, .value = value2 },
	},
	[1] = struct {
		.core_type = 1; /* E-core */
		.pmu_name = xyz_pmu;
		.nr_caps = 1;
		[0] = { .name = cap1, .value = value1 };
	},
};

Does that answer your question?

Thanks for the review,
Ravi