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

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Date:   Fri, 20 May 2022 10:50:45 +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


On 20-May-22 10:01 AM, Ian Rogers wrote:
> On Thu, May 19, 2022 at 8:49 PM Ravi Bangoria <ravi.bangoria@....com> wrote:
>>
>> 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
> 
> I may be being a little ahead of the current code as I'm wondering
> about heterogeneous systems with many non-CPU PMUs. It seems such a
> scenario just wouldn't touch the core_type field here. Could the p or
> e core-ness of a PMU be implied by the name?

Using just pmu_name to identify the type of core it belongs to; yeah
that might work assuming perf_pmu_register() doesn't allow registering
multiple pmus with the same name. I'll remove 'core_type'.

> Is there something similar to core_type in sysfs

I don't think so. I don't have any Intel ADL or ARM big.LITTLE system
to try. But that's not required now.

Thanks,
Ravi