linux-kernel - Re: [PATCH 11/52] perf tools: Add stat config event

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Date:	Tue, 27 Oct 2015 10:44:40 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Jiri Olsa <jolsa@...nel.org>, lkml <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Liang, Kan" <kan.liang@...el.com>
Subject: Re: [PATCH 11/52] perf tools: Add stat config event

Em Tue, Oct 27, 2015 at 02:30:43PM +0100, Jiri Olsa escreveu:
> On Tue, Oct 27, 2015 at 10:16:05AM -0300, Arnaldo Carvalho de Melo wrote:
> > Em Sun, Oct 25, 2015 at 03:51:27PM +0100, Jiri Olsa escreveu:
> > > Adding stat config event to pass/store stat config data,
> > > so report tools (report/script) know how to interpret
> > > stat data.
> > > 
> > > The config data are stored in 'tag|value' way to allow
> > > easy extension and backward compatibility.
> > 
> > I wonder if this couldn't be renamed 'PERF_RECORD_CONFIG' and just go
> > on using one of those 2^64-1 tags for the 'stat config' needs, but then
> > this is just a matter of changing the name of this event, which won't
> > break anything when done.
> 
> we use this event to update 'struct perf_stat_config',
> so it's kind of stat specific

What makes it specific? Isn't this just tag/value? If it was generic all
it would take would be for us to register a range of values (or several)
to be handled by the stat config reading routine.
 
> > Other stuff we may want to have stored like this include sysctl, sysfs
> > values, kernel command line options used, etc.
> 
> I think we could easily add record specific event for this
> once it's needed.. there's plenty of free numbers in user
> events area ;-)

Shhh, don't ask PeterZ about it ;-)

But seriously, what makes this specific? Do you envision the stat code
needing 2^64-1 tags?

Anyway, we can revisit this when code needing to store tag/value
appears.

- Arnaldo
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