* Waiman Long <waiman.l...@hp.com> wrote: > On 05/07/2013 03:01 AM, Ingo Molnar wrote: > >* Waiman Long<waiman.l...@hp.com> 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. > >> > >>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 > >Very nice! > > > >I noticed that you used gprof to instrument perf itself on a call graph > >level. > > > >Does this method of profiling perf via perf: > > > > perf record -g perf report > > perf report > > > >... produce similarly useful call-graph instrumentation for you? > > > >If not or not quite then could you describe the differences? We could use > >that to further improve perf call-graph profiling. > > Thank for the comment. > > The slowdown that I was trying to fix was in the "perf record" part of > the profiling process, not the "perf report" part. I didn't try > perf-record on perf-record as the performance counters are limited > resources and I don't want resource conflicts to affect the results.
ah, ok. In general two instances of cycles-profiling should work just fine without any resource conflicts. But yeah, with "perf record" that's a valid worry and I can see how you wanted to not worry about that. Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/