Re: perf report feature request: folded stack output

[Brendan Gregg <brendan.d.gregg@gmail.com>]

On Fri, Oct 9, 2015 at 4:33 PM, Milian Wolff <milian.wolff@kdab.com> wrote:
> On Freitag, 9. Oktober 2015 14:24:17 CEST Brendan Gregg wrote:
>> G'Day,
>>
>> Maybe someone would like to code this (if not I hope to find the
>> time); perf report already has the capability to print captured stacks
>> as a call tree. I'd like a new output mode: folded.
>>
>> Flame graphs[1] consume folded stacks. Eg:
>>
>> # git clone https://github.com/brendangregg/FlameGraph
>> # cd FlameGraph
>> # perf record -F 99 -a -g -- sleep 60
>> # perf script | ./stackcollapse-perf.pl | ./flamegraph.pl
>> out.perf-folded > flame.svg
>>
>> The last line is inefficient, and should really be something like:
>>
>> # perf report --folded | ./flamegraph.pl out.perf-folded > flame.svg
>>
>> The folded format is function names separated by semicolons, a space,
>> then the count of occurrences. Eg:
>
> <snip>
>
> Hey Brendan,
>
> did you consider writing a python script to do the folding? It's pretty simple
> nowadays, once you cross the initial bar.
>
> I wrote this for stack collapsing futex locks:
> https://paste.kde.org/p61qxah7d
>
> And this to convert samples to callgrind format to open it in KCacheGrind:
> https://paste.kde.org/pjfwd1e8f
>
> If you combine the stack collapsing in the former with the generic
> process_event hook used in the latter, you should be all set. In my tests, it
> was pretty quick to convert stuff, certainly better than creating strings,
> pushing them to the console, and then parsing that again in perl.
>
> perf script fold | flamegraph.pl > flame.svg
>
> gets pretty close. If you want to test locally, make sure you use `perf script
> -s fold.py` or similar.

Thanks, I did check them out (those links since expired), and that is
an improvement! But I can't help but think that perf report already
has the logic for creating a call tree, and it would be more efficient
if perf could just dump in folded output directly -- without a python
coprocess.

Brendan