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SubjectRe: [PATCH v5 0/5] perf report: Show inline stack
Em Sat, Mar 18, 2017 at 05:41:09PM +0100, Milian Wolff escreveu:
> On Donnerstag, 16. März 2017 22:42:22 CET Jin Yao wrote:
> > v5: Update according to Milian Wolff's comments. It groups by address
> > (then display file/ line), or by function (then display function name).
>
> Thank you Jin, that is really good. I tested it and it works really well for
> me.
>
> Arnaldo, could you please consider merging this? It's an extremely useful
> feature and direly missing from perf so far.

Thanks, applied.

> That said, Jin, here are some observations that could be improved in the
> future (I don't think any of these should hold back merging this feature now):
>
> For the following example code build with "-O2 -g" and recorded with "--call-
> graph dwarf" I observe some output combinations that could potentially be
> improved in the future:
>
> ~~~~~~~~~~~~~~~~~~~~
> #include <complex>
> #include <cmath>
> #include <random>
> #include <iostream>
>
> using namespace std;
>
> int main()
> {
> uniform_real_distribution<double> uniform(-1E5, 1E5);
> default_random_engine engine;
> double s = 0;
> for (int i = 0; i < 10000000; ++i) {
> s += norm(complex<double>(uniform(engine), uniform(engine)));
> }
> cout << s << '\n';
> return 0;
> }
> ~~~~~~~~~~~~~~~~
>
> #1 duplicated entries when grouping by function:
>
> ~~~~~~~~~~~~~~~~
> perf report --inline --stdio
> ...
> --35.34%--_start
> __libc_start_main
> main
> main (inline)
> std::uniform_real_distribution<double>::operator()<std::linear_congruential_engine<unsigned
> long, 16807ul, 0ul, 2147483647ul> > (inline)
> std::uniform_real_distribution<double>::operator()<std::linear_congruential_engine<unsigned
> long, 16807ul, 0ul, 2147483647ul> > (inline)
> std::__detail::_Adaptor<std::linear_congruential_engine<unsigned
> long, 16807ul, 0ul, 2147483647ul>, double>::operator() (inline)
> ~~~~~~~~~~~~~~~~
>
> Here, we see main twice, once for the "real" frame, and once for an inlined
> one? Then we see the same function twice as inlined frame, which is also odd.
>
> ~~~~~~~~~~~~~~~~
> perf report --inline --stdio --no-children
> ...
> 59.81% cpp-inlining libm-2.25.so [.] __hypot_finite
> |
> ---__hypot_finite
> hypot
> main
> std::norm<double> (inline)
> main (inline)
> __libc_start_main
> _start
> ~~~~~~~~~~~~~~~~
>
> Here we see a confusing output. The first "main" frame below "hypot" is
> actually code form cpp's complex header which got inlined into main. That
> associates the wrong function name to this frame, i.e. "main" instead of
> std::norm". When the inline stack is shown below we actually see what happens,
> i.e. we eventually end up in main again, but of course this output is not the
> best as-is.
>
> But, again: I think these are minor issues, and the feature itself is already
> extremely useful and I hope to see it finally merged.
>
> Thanks again Jin for your good work!
>
> Cheers
>
> --
> Milian Wolff | milian.wolff@kdab.com | Software Engineer
> KDAB (Deutschland) GmbH&Co KG, a KDAB Group company
> Tel: +49-30-521325470
> KDAB - The Qt Experts


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