Re: [PATCH v2 11/14] perf report: cache srclines for callchain nodes

From: Milian Wolff
Date: Thu Aug 10 2017 - 07:51:49 EST


On Donnerstag, 10. August 2017 04:13:25 CEST Namhyung Kim wrote:
> Hi Milian,
>
> On Sun, Aug 06, 2017 at 11:24:43PM +0200, Milian Wolff wrote:
> > On one hand this ensures that the memory is properly freed when
> > the DSO gets freed. On the other hand this significantly speeds up
> > the processing of the callchain nodes when lots of srclines are
> > requested. For one of my data files e.g.:
> >
> > Before:
> > Performance counter stats for 'perf report -s srcline -g srcline --
stdio':
> > 52496.495043 task-clock (msec) # 0.999 CPUs utilized
> >
> > 634 context-switches # 0.012 K/sec
> >
> > 2 cpu-migrations # 0.000 K/sec
> >
> > 191,561 page-faults # 0.004 M/sec
> >
> > 165,074,498,235 cycles # 3.144 GHz
> > 334,170,832,408 instructions # 2.02 insn per
> > cycle
> >
> > 90,220,029,745 branches # 1718.591 M/sec
> >
> > 654,525,177 branch-misses # 0.73% of all
> > branches
> >
> > 52.533273822 seconds time elapsedProcessed 236605 events and lost 40
> > chunks!>
> > After:
> > Performance counter stats for 'perf report -s srcline -g srcline --
stdio':
> > 22606.323706 task-clock (msec) # 1.000 CPUs utilized
> >
> > 31 context-switches # 0.001 K/sec
> >
> > 0 cpu-migrations # 0.000 K/sec
> >
> > 185,471 page-faults # 0.008 M/sec
> >
> > 71,188,113,681 cycles # 3.149 GHz
> >
> > 133,204,943,083 instructions # 1.87 insn per
> > cycle
> >
> > 34,886,384,979 branches # 1543.214 M/sec
> >
> > 278,214,495 branch-misses # 0.80% of all
> > branches
> >
> > 22.609857253 seconds time elapsed
> >
> > Note that the difference is only this large when `--inline` is not
> > passed. In such situations, we would use the inliner cache and
> > thus do not run this code path that often.
> >
> > I think that this cache should actually be used in other places, too.
> > When looking at the valgrind leak report for perf report, we see tons
> > of srclines being leaked, most notably from calls to
> > hist_entry__get_srcline. The problem is that get_srcline has many
> > different formatting options (show_sym, show_addr, potentially even
> > unwind_inlines when calling __get_srcline directly). As such, the
> > srcline cannot easily be cached for all calls, or we'd have to add
> > caches for all formatting combinations (6 so far). An alternative
> > would be to remove the formatting options and handle that on a
> > different level - i.e. print the sym/addr on demand wherever we
> > actually output something. And the unwind_inlines could be moved into
> > a separate function that does not return the srcline.
>
> Agreed. Also I guess no need to unwind anymore to get a srcfile for
> an entry with your change.

Does this mean I should respin the patch series with the above changes
integrated? Or can we get this in first and then continue with the cleanup as
described above later on?

Thanks

--
Milian Wolff | milian.wolff@xxxxxxxx | Senior Software Engineer
KDAB (Deutschland) GmbH&Co KG, a KDAB Group company
Tel: +49-30-521325470
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