Re: Wrong Perf Backtraces

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On Dienstag, 31. März 2020 17:02:37 CEST ahmadkhorrami wrote:
> Hi Milian,
> Thanks for the detailed answer. Well, the bug you mentioned is bad news.
> Because I sample using uppp. Perhaps this leads to these weird traces.

Please read the full thread from here on:

But as I said - it should be easy to check if this is really the issue are 
running into or not: Try to see if you see the problem when you sample without 
`ppp`. If not, then you can be pretty sure it's this issue. If you still see 
it, then it's something different.

> Is this a purely software bug?

I wouldn't call it that, personally. Rather, it's a limitation in the hardware 
and software. We would need something completely different to "fix" this, i.e. 
something like a deeper LBR. That's btw another alternative you could try: 
`perf record --call-graph lbr` and live with the short call stacks. But at 
least these should be correct (afaik). For me personally they are always far 
too short and thus not practical to use in reality.


Milian Wolff | milian.wolff@xxxxxxxx | Senior Software Engineer
KDAB (Deutschland) GmbH, a KDAB Group company
Tel: +49-30-521325470
KDAB - The Qt, C++ and OpenGL Experts

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