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

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Date:	Thu, 09 May 2013 10:46:07 -0400
From:	Waiman Long <Waiman.Long@...com>
To:	Jiri Olsa <jolsa@...hat.com>
CC:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Stephane Eranian <eranian@...gle.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>
Subject: Re: [PATCH] perf: fix symbol processing bug and greatly improve performance

On 05/09/2013 06:19 AM, Jiri Olsa 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);
>
> otherwise it looks ok:
>
> Acked-by: Jiri Olsa<jolsa@...hat.com>

I am sorry that I forgot to rerun checkpatch.pl again after changing the 
argument type from int to bool. So I missed this warning.

I had resent an updated patch with the warning fixed. I also made some 
update to the patch description.

Regards,
Longman
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