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    SubjectRe: [PATCH] perf top: Make -g refer to callchains
    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.

    - Arnaldo


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