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
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