Re: Callgraph access from python script

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

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On Montag, 28. September 2015 23:08:39 CEST Milian Wolff wrote:
> On Montag, 28. September 2015 19:12:27 CEST Milian Wolff wrote:
> > Hey all,
> > 
> > This was asked before, but I still cannot find any good documentation on
> > the matter. How does one access the callgraph from a python script
> > generated by perf script? The export-to-postgresql.py seems to indicate
> > that this feature was added, but the code is too convoluted for me to
> > grasp.
> > 
> > Looking at the code for trace-event-python.c I see that there is a
> > common_callchain, but I don't get such code generate:
> > 
> > perf record --call-graph dwarf kwrite
> > perf script -g python
> > 
> > the result is: https://paste.kde.org/p0uazuubi
> > 
> > Note how the `while ((event = trace_find_next_event(pevent, event)))` loop
> > has not triggered any output. The reason is that pevent is NULL - where is
> > that supposed to be set when looking at builtin-script.c?
> > 
> > Can someone explain me what I'm doing wrong? Can someone reproduce the odd
> > behavior above?
> 
> OK, so it seems the above only cares for trace points, as the name suggests.
> I.e. it works for files where I trace e.g. -e syscalls:sys_enter_open.
> 
> Why is it not possible to script perf for data obtained from counters? I'd
> hoped to use that to convert the perf output to callgrind format, in order
> to open it with kcachegrind.
> 
> Considering that `perf script` without any arguments prints out all the
> required information, I can of course write a wrapper script around it, but
> using it directly would have been much better.

Studying the code further I stumbled upon process_event which seems to do what 
I want. At least that function get a dict with all information, including 
callchain, and also works with perf data files obtained from a counter.

Could someone please document that?

Thanks
-- 
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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