Re: Accessing sample data (like period) for trace events from python scripts

[Milian Wolff <milian.wolff@kdab.com>]

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On Freitag, 19. August 2016 10:51:01 CEST Namhyung Kim wrote:
> On Fri, Aug 19, 2016 at 10:35:49AM +0900, Namhyung Kim wrote:
> > On Wed, Aug 17, 2016 at 10:48:31AM +0200, Milian Wolff wrote:
> > > On Wednesday, August 17, 2016 12:05:53 PM CEST Namhyung Kim wrote:
> > > > Hi Milian,
> > > > 
> > > > On Tue, Aug 16, 2016 at 08:42:01PM +0200, Milian Wolff wrote:
> > > > > Hey all,
> > > > > 
> > > > > It doesn't seem to be possible to access the period, tid and various
> > > > > other
> > > > > sample fields from a python (and perl?) script using `perf script`.
> > > > > My
> > > > > use-
> > > > > case would be analyzing a perf data file created by perf inject
> > > > > --sched-stat.
> > > > 
> > > > I think you can access param_dict["sample"]["period"].
> > > 
> > > No, that is not possible, but would be a viable solution as well.
> > 
> > Sorry for late reply.  Oh, you wanted to access period of tracepoint
> > but I guess it's always 1, no?
> 
> OK, it seems sched_stat events have periods bigger than 1.  But you
> can access it using 'runtime' or 'delay' field in the event too.  I
> think sample data of tracepoint event is mostly meaningless and you
> should access to the event fields for useful information.  That's why
> it doesn't provide the info for tracepoint events, I guess.
>
> What do you specifically want to know from sample data?

Using `perf inject --sched-stat`, I can get the sched_stat event period to the 
sched_switch event (which has the proper backtrace). That is the data I want 
to access. This is doable when I run:

perf script -F event,period

But it is not accessible from Perl or Python.

Note: the runtime/delay fields are not translated by perf inject, it simply 
sets the period which is then used by the other perf tools.

I really think it should be made possible to access that data from Python/
Perl.

Cheers
-- 
Milian Wolff | milian.wolff@kdab.com | Software Engineer
KDAB (Deutschland) GmbH&Co KG, a KDAB Group company
Tel: +49-30-521325470
KDAB - The Qt Experts

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