linux-kernel - Re: [PATCH v1 1/2] perf auxtrace: Add 'T' itrace option for timestamp trace

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Date:   Thu, 19 Oct 2023 19:52:31 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     James Clark <james.clark@....com>
Cc:     John Garry <john.g.garry@...cle.com>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>
Subject: Re: [PATCH v1 1/2] perf auxtrace: Add 'T' itrace option for
 timestamp trace

On Thu, Oct 19, 2023 at 11:31:16AM +0100, James Clark wrote:

[...]

> > --- a/tools/perf/Documentation/itrace.txt
> > +++ b/tools/perf/Documentation/itrace.txt
> > @@ -25,6 +25,7 @@
> >  		q	quicker (less detailed) decoding
> >  		A	approximate IPC
> >  		Z	prefer to ignore timestamps (so-called "timeless" decoding)
> > +		T	use the timestamp trace as kernel time
> >  
> 
> Maybe "Treat hardware timestamps as kernel time (trace and CPU time use
> same clock source)" would be clearer.

Agreed.

> And another point, although this isn't really related to this patch, but
> why do we have the single letter arguments for itrace? It seems like it
> massively restricts the available options and makes the command lines
> hard to read because they don't have long forms. Why not just have them
> as normal arguments?

TBH, I tried a bit for adding a normal argument, but I found it's not
nature like itrace option for passing the normal argument into the
decoder.  And if we add a normal argument, we need to consider adding
into perf commands for 'perf report', 'perf script', etc; itrace options
can be shared by perf output commands.

I understand an advantage of using normal argument is the 'perf report'
command (e.g. perf report --aux-trace-kernel-time) doesn't need to
specify any extra itrace option.

If anyone still has concern for adding itrace optiona and prefer to add
normal argument, I am happy to rework for adding normal argument.

> If it's a backwards compatibility thing, would there be any objection to
> adding this new option as a normal one rather than an itrace one?

backward compatibility would not a problem - we add a new feature and
at meantime we don't break anything.

> >  	The default is all events i.e. the same as --itrace=iybxwpe,
> >  	except for perf script where it is --itrace=ce
> > diff --git a/tools/perf/util/auxtrace.c b/tools/perf/util/auxtrace.c
> > index a0368202a746..f528c4364d23 100644
> > --- a/tools/perf/util/auxtrace.c
> > +++ b/tools/perf/util/auxtrace.c
> > @@ -1638,6 +1638,9 @@ int itrace_do_parse_synth_opts(struct itrace_synth_opts *synth_opts,
> >  		case 'Z':
> >  			synth_opts->timeless_decoding = true;
> >  			break;
> > +		case 'T':
> > +			synth_opts->use_timestamp = true;
> > +			break;
> >  		case ' ':
> >  		case ',':
> >  			break;
> > diff --git a/tools/perf/util/auxtrace.h b/tools/perf/util/auxtrace.h
> > index 29eb82dff574..55702215a82d 100644
> > --- a/tools/perf/util/auxtrace.h
> > +++ b/tools/perf/util/auxtrace.h
> > @@ -99,6 +99,7 @@ enum itrace_period_type {
> >   * @remote_access: whether to synthesize remote access events
> >   * @mem: whether to synthesize memory events
> >   * @timeless_decoding: prefer "timeless" decoding i.e. ignore timestamps
> > + * @use_timestamp: use the timestamp trace as kernel time
> >   * @vm_time_correlation: perform VM Time Correlation
> >   * @vm_tm_corr_dry_run: VM Time Correlation dry-run
> >   * @vm_tm_corr_args:  VM Time Correlation implementation-specific arguments
> > @@ -146,6 +147,7 @@ struct itrace_synth_opts {
> >  	bool			remote_access;
> >  	bool			mem;
> >  	bool			timeless_decoding;
> > +	bool			use_timestamp;
> 
> And then this one could be like "hw_time_is_kernel_time", but I'm
> stuggling to think of something shorter. Maybe your one is fine along
> with the comment.

It's fine for me to rename as "hw_time_is_kernel_time" for more
readable.  Will do in next spin.

Thanks,
Leo