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

From: Jiri Olsa
Date: Thu May 09 2013 - 06:19:42 EST


On Wed, May 08, 2013 at 11:44:35AM -0400, Waiman Long wrote:
> 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?

I got this from scripts/checkpatch.pl:

WARNING: line over 80 characters
#104: FILE: tools/perf/util/dso.h:136:
+struct dso *dsos__find(struct list_head *head, const char *name, bool
cmp_short);

otherwise it looks ok:

Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>

thanks,
jirka
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