linux-kernel - Re: [PATCH V4 00/11] perf/core: Add ability for an event to "pause" or "resume" AUX area tracing

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Date: Thu, 1 Feb 2024 16:29:27 +0000
From: James Clark <james.clark@....com>
To: Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Mark Rutland <mark.rutland@....com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Heiko Carstens <hca@...ux.ibm.com>, Thomas Richter <tmricht@...ux.ibm.com>,
 Hendrik Brueckner <brueckner@...ux.ibm.com>,
 Suzuki K Poulose <suzuki.poulose@....com>, Mike Leach
 <mike.leach@...aro.org>, coresight@...ts.linaro.org,
 linux-arm-kernel@...ts.infradead.org, Yicong Yang
 <yangyicong@...ilicon.com>, Jonathan Cameron <jonathan.cameron@...wei.com>,
 Will Deacon <will@...nel.org>, Arnaldo Carvalho de Melo <acme@...nel.org>,
 Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
 linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH V4 00/11] perf/core: Add ability for an event to "pause"
 or "resume" AUX area tracing



On 31/01/2024 16:53, Ian Rogers wrote:
> On Mon, Jan 29, 2024 at 4:49 AM Adrian Hunter <adrian.hunter@...el.com> wrote:
>>
>> On 11/01/24 10:19, Adrian Hunter wrote:
>>> Hi
>>>
>>> Hardware traces, such as instruction traces, can produce a vast amount of
>>> trace data, so being able to reduce tracing to more specific circumstances
>>> can be useful.
>>>
>>> The ability to pause or resume tracing when another event happens, can do
>>> that.
>>>
>>> These patches add such a facilty and show how it would work for Intel
>>> Processor Trace.
>>>
>>> Maintainers of other AUX area tracing implementations are requested to
>>> consider if this is something they might employ and then whether or not
>>> the ABI would work for them.
>>>
>>> Changes to perf tools are now (since V4) fleshed out.
>>>
>>>
>>> Changes in V4:
>>>
>>>     perf/core: Add aux_pause, aux_resume, aux_start_paused
>>>       Rename aux_output_cfg -> aux_action
>>>       Reorder aux_action bits from:
>>>               aux_pause, aux_resume, aux_start_paused
>>>       to:
>>>               aux_start_paused, aux_pause, aux_resume
>>>       Fix aux_action bits __u64 -> __u32
>>>
>>>     coresight: Have a stab at support for pause / resume
>>>       Dropped
>>>
>>>     perf tools
>>>       All new patches
>>>
>>> Changes in RFC V3:
>>>
>>>     coresight: Have a stab at support for pause / resume
>>>       'mode' -> 'flags' so it at least compiles
>>>
>>> Changes in RFC V2:
>>>
>>>       Use ->stop() / ->start() instead of ->pause_resume()
>>>       Move aux_start_paused bit into aux_output_cfg
>>>       Tighten up when Intel PT pause / resume is allowed
>>>       Add an example of how it might work for CoreSight
>>
>> Any more comments?
> 
> I think the tools side looks good. The parsing changes match the
> existing style. I wonder if it wouldn't be better to handle the valid
> strings (pause, resume, etc.) in the lexer rather than a separate
> parse function, but the pattern used matches the existing one. You can
> have my Acked-by on the tools changes, although the subtleties of ARM
> PMUs makes me somewhat nervous in this regard.
> 
> Thanks,
> Ian

Acked-by: James Clark <james.clark@....com>

I will get round to adding the Coresight support at some point. I
checked the new parsing in this version and it seems to work ok.