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SubjectRe: [PATCH] perf top: Make -g refer to callchains
On Mon, Nov 18, 2013 at 09:59:45AM -0300, Arnaldo Carvalho de Melo wrote:
> Em Fri, Nov 15, 2013 at 06:46:09AM +0100, Ingo Molnar escreveu:
> > btw., here's some 'perf top' call graph performance and profiling
> > quality feedback, with the latest perf code:
> >
> > 'perf top --call-graph fp' now works very well, using just 0.2%
> > of CPU time on a fast system:
> >
> > 4676 mingo 20 0 612m 56m 9948 S 1 0.2 0:00.68 perf
> >
> > 'perf top --call-graph dwarf' on the other hand is horrendously
> > slow, using 20% of CPU time on a 4 GHz CPU:
> >
> > PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
> > 4646 mingo 20 0 658m 81m 12m R 19 0.3 0:18.17 perf
> >
> > On another system with a 2.4GHz CPU it's taking up 100% of CPU
> > time (!):
> >
> > PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
> > 8018 mingo 20 0 290320 45220 8520 R 99.5 0.3 0:58.81 perf
> >
> > Profiling 'perf top' shows all sorts of very high dwarf
> > processing overhead:
>
> Yeah, top dwarf callchain has been so far a proof of concept, it
> exacerbates problems that can be seen on 'report', but since its live,
> we can see it more clearly.
>
> The work on improving callchain processing, (rb_tree'ing, new comm
> infrastructure) alleviated the problem a bit.
>
> Tuning the stack size requested from the kernel and using --max-stack
> can help when it is really needed, but yes, work on it is *badly* needed.

agreed ;-)

also there's new remote unwind interface recently added
into libdw, which seems to be faster than libunwind.
I plan on adding this soon.

jirka


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