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

From: Jiri Olsa
Date: Tue May 07 2013 - 05:31:13 EST


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..

thanks,
jirka
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