Re: [PATCH] perf: fix symbol processing bug and greatly improve performance

[Waiman Long]

On 05/07/2013 05:30 AM, Jiri Olsa wrote:
> On Mon, May 06, 2013 at 09:43:53AM -0400, Waiman Long wrote:
> > When "perf record" was used on a large machine with a lot of CPUs,
> > the perf post-processing time could take a lot of minutes and even
> > hours depending on how large the resulting perf.data file was.
> >
> > While running AIM7 1500-user high_systime workload on a 80-core x86-64
> > system with a 3.9 kernel, the workload itself took about 2 minutes
> > to run and the perf.data file had a size of 1108.746 MB. However,
> > the post-processing step took more than 10 minutes.
> >
> > With a gprof-profiled perf binary, the time spent by perf was as
> > follows:
> >
> >    %   cumulative   self              self     total
> >   time   seconds   seconds    calls   s/call   s/call  name
> >   96.90    822.10   822.10   192156     0.00     0.00  dsos__find
> >    0.81    828.96     6.86 172089958     0.00     0.00  rb_next
> >    0.41    832.44     3.48 48539289     0.00     0.00  rb_erase
> >
> > So 97% (822 seconds) of the time was spent in a single dsos_find()
> > function. After analyzing the call-graph data below:
> >
> > -----------------------------------------------
> >                  0.00  822.12  192156/192156      map__new [6]
> > [7]     96.9    0.00  822.12  192156         vdso__dso_findnew [7]
> >                822.10    0.00  192156/192156      dsos__find [8]
> >                  0.01    0.00  192156/192156      dsos__add [62]
> >                  0.01    0.00  192156/192366      dso__new [61]
> >                  0.00    0.00       1/45282525     memdup [31]
> >                  0.00    0.00  192156/192230      dso__set_long_name [91]
> > -----------------------------------------------
> >                822.10    0.00  192156/192156      vdso__dso_findnew [7]
> > [8]     96.9  822.10    0.00  192156         dsos__find [8]
> > -----------------------------------------------
> >
> > It was found that the vdso__dso_findnew() function failed to locate
> > VDSO__MAP_NAME ("[vdso]") in the dso list and have to insert a new
> > entry at the end for 192156 times. This problem is due to the fact that
> > there are 2 types of name in the dso entry - short name and long name.
> > The initial dso__new() adds "[vdso]" to both the short and long names.
> > After that, vdso__dso_findnew() modifies the long name to something
> > like /tmp/perf-vdso.so-NoXkDj. The dsos__find() function only compares
> > the long name. As a result, the same vdso entry is duplicated many
> > time in the dso list. This bug increases memory consumption as well
> > as slows the symbol processing time to a crawl.
> hi,
> the issue is there and fix looks ok, thanks!
>
> though I'm not able to get vdso callchains to pop out
> even by investigating report with vdso heavy workload.
>
> I'll have a closer look..

Is there a chance that the fix will go to v3.10 or have to wait for v3.11?

Regards,
Longman
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