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

[Namhyung Kim <namhyung@kernel.org>]

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?

Thanks,
Namhyung


> 
> > 
> > ~~~~~~~~~~~~~~~~~~
> > /tmp$ cat perf-script.py
> > 
> > import os
> > import sys
> > 
> > sys.path.append(os.environ['PERF_EXEC_PATH'] + \
> >         '/scripts/python/Perf-Trace-Util/lib/Perf/Trace')
> > 
> > from perf_trace_context import *
> > from Core import *
> > 
> > def trace_unhandled(event_name, context, event_fields_dict):
> >         print event_fields_dict['sample']['period']
> > 
> > /tmp$ perf script -s perf-script.py
> > Traceback (most recent call last):
> >   File "perf-script.py", line 11, in trace_unhandled
> >     print event_fields_dict['sample']['period']
> > KeyError: 'sample'
> > Fatal Python error: problem in Python trace event handler
> > Aborted (core dumped)
> > ~~~~~~~~~~~~~~~~~~
> > 
> > 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
> 
>