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