Messages in this thread | | | Date | Fri, 05 Jul 2013 13:09:17 -0400 | From | Waiman Long <> | Subject | Re: [PATCH v2] perf record: fix symbol processing bug and greatly improve performance |
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On 05/10/2013 04:12 AM, Ingo Molnar wrote: > * Waiman Long<Waiman.Long@hp.com> wrote: > >> When "perf record" was used on a large machine with a lot of CPUs, >> the perf post-processing time (the time after the workload was done >> until the perf command itself exited) 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 (with only the -s -a options used), >> 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. >> >> To resolve this problem, the dsos__find() function interface was >> modified to enable searching either the long name or the short >> name. The vdso__dso_findnew() will now search only the short name >> while the other call sites search for the long name as before. >> >> With this change, the cpu time of perf was reduced from 848.38s to >> 15.77s and dsos__find() only accounted for 0.06% of the total time. >> >> 0.06 15.73 0.01 192151 0.00 0.00 dsos__find >> >> Signed-off-by: Waiman Long<Waiman.Long@hp.com> >> --- >> tools/perf/util/dso.c | 10 ++++++++-- >> tools/perf/util/dso.h | 3 ++- >> tools/perf/util/vdso.c | 2 +- >> 3 files changed, 11 insertions(+), 4 deletions(-) > Acked-by: Ingo Molnar<mingo@kernel.org> > > Thanks, > > Ingo
Thank for the Ack. Will that patch go into v3.11?
Regards, Longman
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