Re: [PATCH v3 01/18] perf metricgroup: Add care to picking the evsel for displaying a metric

Mi, Dapeng
2025-11-12T08:14:43Z

On 11/12/2025 3:05 AM, Namhyung Kim wrote:
> On Tue, Nov 11, 2025 at 09:20:30AM -0800, Ian Rogers wrote:
>> On Tue, Nov 11, 2025 at 12:15 AM Mi, Dapeng <dapeng1.mi@linux.intel.com> wrote:
>>>
>>> On 11/11/2025 12:04 PM, Ian Rogers wrote:
>>>> Rather than using the first evsel in the matched events, try to find
>>>> the least shared non-tool evsel. The aim is to pick the first evsel
>>>> that typifies the metric within the list of metrics.
>>>>
>>>> This addresses an issue where Default metric group metrics may lose
>>>> their counter value due to how the stat displaying hides counters for
>>>> default event/metric output.
>>>>
>>>> For a metricgroup like TopdownL1 on an Intel Alderlake the change is,
>>>> before there are 4 events with metrics:
>>>> ```
>>>> $ perf stat -M topdownL1 -a sleep 1
>>>>
>>>> Performance counter stats for 'system wide':
>>>>
>>>> 7,782,334,296 cpu_core/TOPDOWN.SLOTS/ # 10.4 % tma_bad_speculation
>>>> # 19.7 % tma_frontend_bound
>>>> 2,668,927,977 cpu_core/topdown-retiring/ # 35.7 % tma_backend_bound
>>>> # 34.1 % tma_retiring
>>>> 803,623,987 cpu_core/topdown-bad-spec/
>>>> 167,514,386 cpu_core/topdown-heavy-ops/
>>>> 1,555,265,776 cpu_core/topdown-fe-bound/
>>>> 2,792,733,013 cpu_core/topdown-be-bound/
>>>> 279,769,310 cpu_atom/TOPDOWN_RETIRING.ALL/ # 12.2 % tma_retiring
>>>> # 15.1 % tma_bad_speculation
>>>> 457,917,232 cpu_atom/CPU_CLK_UNHALTED.CORE/ # 38.4 % tma_backend_bound
>>>> # 34.2 % tma_frontend_bound
>>>> 783,519,226 cpu_atom/TOPDOWN_FE_BOUND.ALL/
>>>> 10,790,192 cpu_core/INT_MISC.UOP_DROPPING/
>>>> 879,845,633 cpu_atom/TOPDOWN_BE_BOUND.ALL/
>>>> ```
>>>>
>>>> After there are 6 events with metrics:
>>>> ```
>>>> $ perf stat -M topdownL1 -a sleep 1
>>>>
>>>> Performance counter stats for 'system wide':
>>>>
>>>> 2,377,551,258 cpu_core/TOPDOWN.SLOTS/ # 7.9 % tma_bad_speculation
>>>> # 36.4 % tma_frontend_bound
>>>> 480,791,142 cpu_core/topdown-retiring/ # 35.5 % tma_backend_bound
>>>> 186,323,991 cpu_core/topdown-bad-spec/
>>>> 65,070,590 cpu_core/topdown-heavy-ops/ # 20.1 % tma_retiring
>>>> 871,733,444 cpu_core/topdown-fe-bound/
>>>> 848,286,598 cpu_core/topdown-be-bound/
>>>> 260,936,456 cpu_atom/TOPDOWN_RETIRING.ALL/ # 12.4 % tma_retiring
>>>> # 17.6 % tma_bad_speculation
>>>> 419,576,513 cpu_atom/CPU_CLK_UNHALTED.CORE/
>>>> 797,132,597 cpu_atom/TOPDOWN_FE_BOUND.ALL/ # 38.0 % tma_frontend_bound
>>>> 3,055,447 cpu_core/INT_MISC.UOP_DROPPING/
>>>> 671,014,164 cpu_atom/TOPDOWN_BE_BOUND.ALL/ # 32.0 % tma_backend_bound
>>>> ```
>>> It looks the output of cpu_core and cpu_atom events are mixed together,
>>> like the "cpu_core/INT_MISC.UOP_DROPPING/". Could we resort the events and
>>> separate the cpu_core and cpu_atom events output? It would make the output
>>> more read-friendly. Thanks.
>> So the metrics are tagged as to not group the events:
>> https://web.git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/pmu-events/arch/x86/alderlake/adl-metrics.json?h=perf-tools-next#n117
>> Running with each metric causes the output to be:
>> ```
>> $ perf stat -M tma_bad_speculation,tma_backend_bound,tma_frontend_bound,tma_retiring
>> -a sleep 1
>>
>> Performance counter stats for 'system wide':
>>
>> 1,615,145,897 cpu_core/TOPDOWN.SLOTS/ # 8.1 %
>> tma_bad_speculation
>> # 42.5 %
>> tma_frontend_bound (49.89%)
>> 243,037,087 cpu_core/topdown-retiring/ # 34.5 %
>> tma_backend_bound (49.89%)
>> 129,341,306 cpu_core/topdown-bad-spec/
>> (49.89%)
>> 2,679,894 cpu_core/INT_MISC.UOP_DROPPING/
>> (49.89%)
>> 696,940,348 cpu_core/topdown-fe-bound/
>> (49.89%)
>> 563,319,011 cpu_core/topdown-be-bound/
>> (49.89%)
>> 1,795,034,847 cpu_core/slots/
>> (50.11%)
>> 262,140,961 cpu_core/topdown-retiring/
>> (50.11%)
>> 44,589,349 cpu_core/topdown-heavy-ops/ # 14.4 %
>> tma_retiring (50.11%)
>> 160,987,341 cpu_core/topdown-bad-spec/
>> (50.11%)
>> 778,250,364 cpu_core/topdown-fe-bound/
>> (50.11%)
>> 622,499,674 cpu_core/topdown-be-bound/
>> (50.11%)
>> 90,849,750 cpu_atom/TOPDOWN_RETIRING.ALL/ # 8.1 %
>> tma_retiring
>> # 17.2 %
>> tma_bad_speculation
>> 223,878,243 cpu_atom/CPU_CLK_UNHALTED.CORE/
>> 423,068,733 cpu_atom/TOPDOWN_FE_BOUND.ALL/ # 37.8 %
>> tma_frontend_bound
>> 413,413,499 cpu_atom/TOPDOWN_BE_BOUND.ALL/ # 36.9 %
>> tma_backend_bound
>> ```
>> so you can see that it is the effect of not grouping the events that
>> leads to the cpu_core and cpu_atom split.
>>
>> The code that does sorting/fixing/adding of events, primarily to fix
>> topdown, is parse_events__sort_events_and_fix_groups:
>> https://web.git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/parse-events.c?h=perf-tools-next#n2030
>> but I've tried to make that code respect the incoming evsel list order
>> because if a user specifies an order then they generally expect it to
>> be respected (unless invalid or because of topdown events). For
>> --metric-only the event order doesn't really matter.
>>
>> Anyway, I think trying to fix this is out of scope for this patch
>> series, although I agree with you about the readability. The behavior
>> here matches old behavior such as:
>> ```
>> $ perf --version
>> perf version 6.16.12
>> $ perf stat -M TopdownL1 -a sleep 1
>>
>> Performance counter stats for 'system wide':
>>
>> 11,086,754,658 cpu_core/TOPDOWN.SLOTS/ # 27.1 %
>> tma_backend_bound
>> # 7.5 %
>> tma_bad_speculation
>> # 36.5 %
>> tma_frontend_bound
>> # 28.9 %
>> tma_retiring
>> 3,219,475,010 cpu_core/topdown-retiring/
>> 820,655,931 cpu_core/topdown-bad-spec/
>> 418,883,912 cpu_core/topdown-heavy-ops/
>> 4,082,884,459 cpu_core/topdown-fe-bound/
>> 3,012,532,414 cpu_core/topdown-be-bound/
>> 1,030,171,196 cpu_atom/TOPDOWN_RETIRING.ALL/ # 17.4 %
>> tma_retiring
>> # 16.5 %
>> tma_bad_speculation
>> 1,185,093,601 cpu_atom/CPU_CLK_UNHALTED.CORE/ # 29.8 %
>> tma_backend_bound
>> # 36.4 %
>> tma_frontend_bound
>> 2,154,914,153 cpu_atom/TOPDOWN_FE_BOUND.ALL/
>> 14,988,684 cpu_core/INT_MISC.UOP_DROPPING/
>> 1,763,486,868 cpu_atom/TOPDOWN_BE_BOUND.ALL/
>>
>> 1.004103365 seconds time elapsed
>> ```
>> ie the cpu_core and cpu_atom mixing of events isn't a regression
>> introduced here. There isn't a simple fix for the ordering, as we
>> don't want to mess up the non-metric cases. I'm happy if you think
>> things can be otherwise to make a change.
> Agreed and it should be handled in a separate patch (series). Let's fix
> problems one at a time.

It makes sense. Thanks.

>
> Thanks,
> Namhyung
>
>