Hi, thanks for the reply! I have gone down that route, but I don't get user stack traces at all. I suspect this is because I'm on ARM 3.14.52, which does not support CONFIG_USER_STACKTRACE_SUPPORT. Nor does it support CONFIG_ARCH_SUPPORTS_UPROBES. All that said, I DO get stack traces when using straight perf record with "--call-graph dwarf". (Does that imply "-e cpu-clock"?). So, I was hoping that whatever is enabling that event to get stack traces might be available to me. Jonah On Fri, Mar 4, 2016 at 5:05 PM, Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> wrote: > Em Fri, Mar 04, 2016 at 02:15:25PM -0500, Jonah Petri escreveu: >> Hello, >> >> My application is doing realtime low-latency audio, and we're seeing >> occasional dropouts, which we've traced (via ftrace) to an unexplained >> sched_stat_wait event on our audio-handling user thread. >> >> We're really not sure what might be causing this, but if I could get >> the user stack trace causing this event, it would let me see exactly >> the problem. Even the top frame of the stack would be invaluable. >> >> Is there a way to get this info? Preferrably with ftrace, but any >> methods or hints would be much appreciated. > > [root@jouet ~]# perf list *:sched_stat_wait > > List of pre-defined events (to be used in -e): > > sched:sched_stat_wait [Tracepoint event] > > [root@jouet ~]# perf record -a --call-graph dwarf -e sched:*stat_wait > ^C[ perf record: Woken up 1 times to write data ] > [ perf record: Captured and wrote 4.157 MB perf.data (763 samples) ] > > [root@jouet ~]# > [root@jouet ~]# perf report --stdio | head -53 > Failed to open /tmp/perf-7459.map, continuing without symbols > no symbols found in /usr/sbin/rngd, maybe install a debug package? > # To display the perf.data header info, please use --header/--header-only options. > # > # > # Total Lost Samples: 0 > # > # Samples: 763 of event 'sched:sched_stat_wait' > # Event count (approx.): 2027097 > # > # Children Self Trace output > # ........ ........ ............................................... > # > 8.94% 8.94% comm=Xorg pid=2730 delay=181323 [ns] > | > ---entry_SYSCALL_64_fastpath > sys_poll > do_sys_poll > poll_schedule_timeout > schedule_hrtimeout_range > schedule_hrtimeout_range_clock > schedule > __schedule > pick_next_task_fair > set_next_entity > update_stats_wait_end > 0x563bfb142909 > __libc_start_main > main > meta_run > g_main_loop_run > g_main_context_iterate.isra.29 > 0x7fb1060a9fdd > > 4.73% 4.73% comm=gnome-terminal- pid=3412 delay=95977 [ns] > | > ---entry_SYSCALL_64_fastpath > sys_poll > do_sys_poll > poll_schedule_timeout > schedule_hrtimeout_range > schedule_hrtimeout_range_clock > schedule > __schedule > pick_next_task_fair > set_next_entity > update_stats_wait_end > _start > __libc_start_main > main > g_application_run > g_main_context_iteration > g_main_context_iterate.isra.29 > 0x7fd2cbd9bfdd > > [root@jouet ~]# > > Replace 'record -a' with 'record --pid YOUR-PID' or workload, etc, see: > > man perf-record > > If you get some unresolved symbols, install 'gcc -g' built binaries or > -debuginfo packages or equivalent in !fedora/RHEL distros. > > - Arnaldo -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
