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

[Ingo Molnar <mingo@kernel.org>]

* Jiri Olsa <jolsa@redhat.com> wrote:

> 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);

For a prototype line that's OK I think.

Thanks,

	Ingo