On Sunday 14 June 2015 13:02:57 Milian Wolff wrote:
> Hey all,
>
> Some time ago I read this interesting article:
>
> http://article.gmane.org/gmane.linux.kernel/1809078
>
> It mentions a new call stack unwinding for perf, based on Haswell LBR
> facility. I now have a new Laptop with a Broadwell i7-5600U CPU, but my perf
> version 4.0.3 running against a Linux 4.0.4 kernel (all vanilla Archlinux
> versions) does not seem to support this feature. Was it ever included in
> the mainline? Is a special compiler flag required to enable this feature?
> Anything else I'm missing?
>
> callchain: Unknown --call-graph option value: lbr
>
> usage: perf record [<options>] [<command>]
> or: perf record [<options>] -- <command> [<options>]
>
> --call-graph <mode[,dump_size]>
> setup and enables call-graph (stack
> chain/backtrace) recording: fp dwarf
OK, with a more recent perf v4.2.rc5 on a Intel(R) Core(TM) i7-4770 CPU @
3.40GHz it actually works. Somewhat :) It is much faster, but the callstacks
don't terminate properly, and are sometimes not correctly demangled. I observe
the following behavior:
15.56% ex_string_compa libQt5Core.so.5.5.0 [.] QString::compare_helper
|
|--5.84%--
_ZN7QString14compare_helperEPK5QChariS2_iN2Qt15CaseSensitivityE@plt
| QString::compare_helper
| main
| |
| |--4.24%-- main
| | |
| | |--1.60%-- main
| | | |
| | | |--1.07%-- main
| | | | |
| | | | |--0.54%-- main
| | | | | main
| | | | |
| | | | --0.53%--
QString::compare_helper
| | | | main
| | | |
| | | --0.53%--
QString::compare_helper
| | | main
| | | main
| | |
QString::compare_helper
| | | main
| | |
QString::compare_helper
...
The correct callgraph, as shown by --call-graph dwarf, is:
21.62% ex_string_compa libQt5Core.so.5.5.0 [.] QString::compare_helper
|
---QString::compare_helper
main
Is this a known (undocumented) limitation or a bug? Is there anything I could
do to get this fixed?
Thanks
--
Milian Wolff
[email protected]
http://milianw.de
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