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Date: Fri, 10 Feb 2023 21:45:12 +0800 (CST)
From: "David Wang" <00107082@....com>
To: musl@...ts.openwall.com
Cc: "Markus Wichmann" <nullplan@....net>
Subject: Re:Re: Re:Re: Re:Re: qsort
At 2023-02-10 21:10:45, "Rich Felker" <dalias@...c.org> wrote:
>On Fri, Feb 10, 2023 at 06:00:27PM +0800, David Wang wrote:
>What tool was used for this? gprof or anything else invasive is not
>meaningful; for tiny functions, the entire time measured will be the
>profiling overhead. perf(1) is the only way I know to get meaningful
>numbers.
>
>In particular, it makes no sense that significant time was spent in
>wrapper_cmp, which looks like (i386):
>
> 0: ff 64 24 0c jmp *0xc(%esp)
>
>or (x86_64):
>
> 0: ff e2 jmpq *%rdx
>
>or (arm):
>
> 0: 4710 bx r2
>
>but I can imagine it being (relatively) gigantic with a call out to
>profiling code.
>
>Rich
I have myself implemented a profiling tool, using perf_event_open to start profiling and mmap to collect callchains, the source code is here https://github.com/zq-david-wang/linux-tools/blob/main/perf/profiler/profiler.cpp
(Still buggy, there is always strange callchain which I could not figure out...and I am still working on it...)
Also, I did not use any optimization when compile the code, which could make a difference, I will take time to give it a try .
About wrapper_cmp, in my last profiling, there are total 931387 samples collected, 257403 samples contain callchain ->wrapper_cmp, among those 257403 samples, 167410 samples contain callchain ->wrapper_cmp->mycmp,
that is why I think there is extra overhead about wrapper_cmp. Maybe compiler optimization would change the result, and I will make further checks.
David
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