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: Wed, 31 Jan 2024 08:53:06 -0800
From: Ian Rogers <irogers@...gle.com>
To: 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>, 
	James Clark <james.clark@....com>, 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 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