Re: Wrong Perf Backtraces

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On Mon, 23 Mar 2020 00:54:01 +0430
ahmadkhorrami <ahmadkhorrami@xxxxxxxx> wrote:

> Hi,
> I used "Perf" to extract call graphs in an evince benchmark. The command 
> used is as follows:
> sudo perf record -d --call-graph dwarf -c 10000 e 
> mem_load_uops_retired.l3_miss:uppp /opt/evince-3.28.4/bin/evince
> I extracted the backtraces using "perf script" and found out that there 
> are many corrupted backtrace instances. Some contained repeated function 
> calls, for example two consecutive gmallocn()s exactly at the same 
> offsets. There are also some backtraces where the callers and callees do 
> not match.

Could you show some examples of the backtraces you mention?

> Note that that mappings are correct. In other words, each single line of 
> the reported backtraces is correct (i.e., addresses match with 
> functions). But is seems that there are some function calls in the 
> middle, which are missed by "Perf". Strangely, in all runs (and also 
> with different sampling frequencies) the problem occurs exactly at the 
> same place.
> I am really confused and looking forward to any help. I can also send 
> backtraces if needed.

-- Steve

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