Re: Wrong Perf Backtraces

On Mon, Mar 23, 2020 at 07:48:26AM +0430, ahmadkhorrami wrote:
> Here is a link to the detailed question at Stackoverflow: 
> 
> https://stackoverflow.com/questions/60766026/wrong-perf-backtraces 

hi,
what perf version are you running?

jirka


> 
> I can copy it here, if needed. 
> 
> Thanks 
> 
> On 2020-03-23 05:04, Steven Rostedt wrote:
> 
> > On Mon, 23 Mar 2020 00:54:01 +0430
> > ahmadkhorrami <[email protected]> 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