Re: [PATCH v4 0/7] Event parsing fixes

["Liang, Kan" <kan.liang@linux.intel.com>]

On 2024-08-22 11:10 a.m., Ian Rogers wrote:
> On Thu, Aug 22, 2024 at 7:32 AM Liang, Kan <kan.liang@linux.intel.com> wrote:
>>
>>
>>
>> On 2024-08-22 9:24 a.m., James Clark wrote:
>>> I rebased this one and made some other fixes so that I could test it,
>>> so I thought I'd repost it here in case it's helpful. I also added a
>>> new test.
>>>
>>> But for the testing it all looks ok.
>>>
>>> There is one small difference where it now shows "stalled-cycles-..."
>>> as <not supported> events, when before it just didn't show them at all when
>>> they weren't supported:
>>>
>>>   $ perf stat -- true
>>>
>>>   Performance counter stats for 'true':
>>>
>>>               0.66 msec task-clock                       #    0.384 CPUs utilized
>>>                  0      context-switches                 #    0.000 /sec
>>>                  0      cpu-migrations                   #    0.000 /sec
>>>                 52      page-faults                      #   78.999 K/sec
>>>      <not counted>      cpu_atom/instructions/                                                  (0.00%)
>>>            978,399      cpu_core/instructions/           #    1.02  insn per cycle
>>>      <not counted>      cpu_atom/cycles/                                                        (0.00%)
>>>            959,722      cpu_core/cycles/                 #    1.458 GHz
>>>    <not supported>      cpu_atom/stalled-cycles-frontend/
>>>    <not supported>      cpu_core/stalled-cycles-frontend/
>>>
>>
>> Intel didn't support the events for a very long time. It would impact
>> many existing generations and all future generations.
>> The current method is to hide the non-exist events. The TopdownL1 is an
>> example. If it doesn't exist in the json file, perf stat will not
>> display it.
>> I don't think it's a good idea to disclose non-exist events in the perf
>> stat default.
>>
>> The <not supported> doesn't help here, since there could be many reasons
>> that the perf tool fails to open a counter. It just provides a
>> misleading message for an event that never existed.
> 
> The list of "default" events, not metrics, similarly has "<not
> supported>" in many configurations with "-dd" or "-ddd" on AMD. I'm
> not sure the set of default events, at different detail levels, is
> necessarily the best. The default events can also be a source of
> multiplexing, for example, showing branch miss rate alongside topdown
> metrics. Anyway, for the "<not supported>" we should probably be able
> to tweak should_skip_zero_counter that is in stat-display.c and tag
> these default events as "skippable".

The "skippable" should be fine as long as it's completely hidden.

BTW: The stalled-cycles-backend should be similar to the
stalled-cycles-frontend, but it isn't shown in the example. Is the
stalled-cycles-backend event missed?

Thanks,
Kan
> 
> Thanks,
> Ian
> 
>> Thanks,
>> Kan
>>> I don't think that's a big deal though and could probably be fixed up
>>> later if we really want to.
>>>
>>> Tested on Raptor Lake, Juno, N1, Ampere (with the DSU cycles PMU) and
>>> I also faked an Apple M on Juno.
>>>
>>> Changes since v3:
>>>
>>>   * Rebase onto perf-tools-next 6236ebe07
>>>   * Fix Intel TPEBS counting mode test
>>>   * Fix arm-spe build
>>>   * Add support for DT devices in stat test
>>>   * Add a new test for hybrid perf stat default arguments
>>>
>>> Ian Rogers (5):
>>>   perf evsel: Add alternate_hw_config and use in evsel__match
>>>   perf stat: Uniquify event name improvements
>>>   perf stat: Remove evlist__add_default_attrs use strings
>>>   perf evsel x86: Make evsel__has_perf_metrics work for legacy events
>>>   perf evsel: Remove pmu_name
>>>
>>> James Clark (2):
>>>   perf test: Make stat test work on DT devices
>>>   perf test: Add a test for default perf stat command
>>>
>>>  tools/perf/arch/arm64/util/arm-spe.c          |   4 +-
>>>  tools/perf/arch/x86/util/evlist.c             |  74 +----
>>>  tools/perf/arch/x86/util/evsel.c              |  35 ++-
>>>  tools/perf/builtin-diff.c                     |   6 +-
>>>  tools/perf/builtin-stat.c                     | 291 +++++++-----------
>>>  tools/perf/tests/parse-events.c               |   2 +-
>>>  tools/perf/tests/shell/stat.sh                |  33 +-
>>>  .../perf/tests/shell/test_stat_intel_tpebs.sh |  11 +-
>>>  tools/perf/util/evlist.c                      |  46 +--
>>>  tools/perf/util/evlist.h                      |  12 -
>>>  tools/perf/util/evsel.c                       |  28 +-
>>>  tools/perf/util/evsel.h                       |  22 +-
>>>  tools/perf/util/metricgroup.c                 |   4 +-
>>>  tools/perf/util/parse-events.c                |  58 ++--
>>>  tools/perf/util/parse-events.h                |   8 +-
>>>  tools/perf/util/parse-events.y                |   2 +-
>>>  tools/perf/util/pmu.c                         |   6 +-
>>>  tools/perf/util/pmu.h                         |   2 +-
>>>  tools/perf/util/stat-display.c                | 101 ++++--
>>>  tools/perf/util/stat-shadow.c                 |  14 +-
>>>  tools/perf/util/stat.c                        |   2 +-
>>>  21 files changed, 348 insertions(+), 413 deletions(-)
>>>
>