linux-kernel - Re: [PATCH] perf vendor events arm64: Remove uncountable events

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Message-ID: <3513a638-c207-4ce5-b966-b274891beffe@linaro.org>
Date: Mon, 5 Jan 2026 10:23:01 +0000
From: James Clark <james.clark@...aro.org>
To: Ian Rogers <irogers@...gle.com>
Cc: John Garry <john.g.garry@...cle.com>, Will Deacon <will@...nel.org>,
 Mike Leach <mike.leach@...aro.org>, Leo Yan <leo.yan@...ux.dev>,
 Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Jiri Olsa <jolsa@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>,
 Akio Kakuno <fj3333bs@...jp.fujitsu.com>,
 Yoshihiro Furudera <fj5100bi@...itsu.com>, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH] perf vendor events arm64: Remove uncountable events



On 04/01/2026 1:27 am, Ian Rogers wrote:
> On Sat, Jan 3, 2026 at 8:38 AM James Clark <james.clark@...aro.org> wrote:
>>
>>
>>
>> On 02/01/2026 3:29 pm, Ian Rogers wrote:
>>> On Wed, Dec 31, 2025 at 4:13 AM James Clark <james.clark@...aro.org> wrote:
>>>>
>>>> These events are never countable by the PMU and are only intended to
>>>> be used as external inputs to trace. Therefore showing them in 'perf
>>>> list' is misleading so remove them.
>>>
>>> What does "trace" mean in this context?
>>>
>>
>> CPU trace, Either ETE (Embedded Trace Extension) or ETM (Embedded Trace
>> Macrocell). You can select PMU events as inputs to the trace block to
>> make it do things like start and stop tracing.
> 
> Ah ok, trace immediately makes me think of `perf trace` currently.
> Presumably there's no perf integration for ETE and ETM that somehow
> use these event encodings? Looks not and the changes make sense to me.

Not yet, currently you have to create kernel modules to do complex trace 
configs.

> 
> Reviewed-by: Ian Rogers <irogers@...gle.com>
> 
> Thanks,
> Ian
>

Thanks!

>>> Thanks,
>>> Ian
>>>
>>>> The generator script doesn't emit these events when used with the new
>>>> telemetry-solution input files [1].
>>>>
>>>> 'perf list' should only show countable events because there are events
>>>> that are sometimes implemented, sometimes countable and sometimes not,
>>>> for example TRB_TRIG. If we always include any implemented events
>>>> whether they are countable or not then it's not possible to tell whether
>>>> they are usable in perf without going to the docs, defeating the point
>>>> of 'perf list'.
>>>>
>>>> It's also not useful yet to display implemented events that are not
>>>> countable (for help in using trace rather than perf stat), because
>>>> PMU_OVFS and PMU_HOVFS are practically always implemented and TRB_TRIG
>>>> is always implemented when there is TRBE.
>>>>
>>>> [1]: https://gitlab.arm.com/telemetry-solution/telemetry-solution/-/tree/main/data/pmu/cpu
>>>>
>>>> Signed-off-by: James Clark <james.clark@...aro.org>
>>>> ---
>>>>    tools/perf/pmu-events/arch/arm64/arm/cortex-a510/pmu.json  |  8 --------
>>>>    tools/perf/pmu-events/arch/arm64/common-and-microarch.json | 12 ------------
>>>>    tools/perf/pmu-events/arch/arm64/fujitsu/monaka/pmu.json   | 10 ----------
>>>>    3 files changed, 30 deletions(-)
>>>>
>>>> diff --git a/tools/perf/pmu-events/arch/arm64/arm/cortex-a510/pmu.json b/tools/perf/pmu-events/arch/arm64/arm/cortex-a510/pmu.json
>>>> deleted file mode 100644
>>>> index d8b7b9f9e5fa..000000000000
>>>> --- a/tools/perf/pmu-events/arch/arm64/arm/cortex-a510/pmu.json
>>>> +++ /dev/null
>>>> @@ -1,8 +0,0 @@
>>>> -[
>>>> -    {
>>>> -        "ArchStdEvent": "PMU_OVFS"
>>>> -    },
>>>> -    {
>>>> -        "ArchStdEvent": "PMU_HOVFS"
>>>> -    }
>>>> -]
>>>> diff --git a/tools/perf/pmu-events/arch/arm64/common-and-microarch.json b/tools/perf/pmu-events/arch/arm64/common-and-microarch.json
>>>> index 2416d9f8a83d..468cb085d879 100644
>>>> --- a/tools/perf/pmu-events/arch/arm64/common-and-microarch.json
>>>> +++ b/tools/perf/pmu-events/arch/arm64/common-and-microarch.json
>>>> @@ -432,24 +432,12 @@
>>>>            "EventName": "TRB_WRAP",
>>>>            "BriefDescription": "Trace buffer current write pointer wrapped"
>>>>        },
>>>> -    {
>>>> -        "PublicDescription": "PMU overflow, counters accessible to EL1 and EL0",
>>>> -        "EventCode": "0x400D",
>>>> -        "EventName": "PMU_OVFS",
>>>> -        "BriefDescription": "PMU overflow, counters accessible to EL1 and EL0"
>>>> -    },
>>>>        {
>>>>            "PublicDescription": "Trace buffer Trigger Event",
>>>>            "EventCode": "0x400E",
>>>>            "EventName": "TRB_TRIG",
>>>>            "BriefDescription": "Trace buffer Trigger Event"
>>>>        },
>>>> -    {
>>>> -        "PublicDescription": "PMU overflow, counters reserved for use by EL2",
>>>> -        "EventCode": "0x400F",
>>>> -        "EventName": "PMU_HOVFS",
>>>> -        "BriefDescription": "PMU overflow, counters reserved for use by EL2"
>>>> -    },
>>>>        {
>>>>            "PublicDescription": "PE Trace Unit external output 0",
>>>>            "EventCode": "0x4010",
>>>> diff --git a/tools/perf/pmu-events/arch/arm64/fujitsu/monaka/pmu.json b/tools/perf/pmu-events/arch/arm64/fujitsu/monaka/pmu.json
>>>> deleted file mode 100644
>>>> index 65bd6cdd0dd5..000000000000
>>>> --- a/tools/perf/pmu-events/arch/arm64/fujitsu/monaka/pmu.json
>>>> +++ /dev/null
>>>> @@ -1,10 +0,0 @@
>>>> -[
>>>> -    {
>>>> -        "ArchStdEvent": "PMU_OVFS",
>>>> -        "BriefDescription": "This event counts the event generated each time one of the condition occurs described in Arm Architecture Reference Manual for A-profile architecture. This event is only for output to the trace unit."
>>>> -    },
>>>> -    {
>>>> -        "ArchStdEvent": "PMU_HOVFS",
>>>> -        "BriefDescription": "This event counts the event generated each time an event is counted by an event counter <n> and all of the condition occur described in Arm Architecture Reference Manual for A-profile architecture. This event is only for output to the trace unit."
>>>> -    }
>>>> -]
>>>>
>>>> ---
>>>> base-commit: cbd41c6d4c26c161a2b0e70ad411d3885ff13507
>>>> change-id: 20251230-james-perf-uncountable-events-28adfb93b73f
>>>>
>>>> Best regards,
>>>> --
>>>> James Clark <james.clark@...aro.org>
>>>>
>>