Messages in this thread | | | Date | Tue, 7 May 2013 11:30:31 +0200 | From | Jiri Olsa <> | Subject | Re: [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
| |