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