Messages in this thread Patch in this message | | | From | Cheng Jian <> | Subject | [PATCH] perf/ftrace : Fix repetitious traces when specify a target task | Date | Tue, 10 Oct 2017 09:19:39 +0800 |
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When use perf to trace the sched_wakeup and sched_wakeup_new tracepoint, there is a bug that output the same event repetitiously. It can be reproduced by :
perf record -e sched:sched_wakeup_new ./bug_fork
bug_fork is an demo that can generating wakeup_new events :
the parent process does nothing but fork a child process, and then they both quit.
perf script :
bug_fork 1078 [002] 184.669341: sched:sched_wakeup_new: comm=bug_fork pid=1079 prio=120 target_cpu=000 bug_fork 1078 [002] 184.670128: sched:sched_wakeup_new: comm=bug_fork pid=1079 prio=120 target_cpu=000 bug_fork 1078 [002] 184.670128: sched:sched_wakeup_new: comm=bug_fork pid=1079 prio=120 target_cpu=000 bug_fork 1078 [002] 184.670128: sched:sched_wakeup_new: comm=bug_fork pid=1079 prio=120 target_cpu=000 bug_fork 1078 [002] 184.670128: sched:sched_wakeup_new: comm=bug_fork pid=1079 prio=120 target_cpu=000
but ftrace only show one event:
bug_fork-1078 [002] d... 184.889159: sched_wakeup_new: comm=bug_fork pid=1079 prio=120 target_cpu=000
perf script repeat prints wakeup_new events multiple times.
These events which trigger this issue not only monitor the current task, but also specify a target task. For example, the sched_wakeup and sched_wakeup_new tracepoint will be caught when the current task wakeup the target task which we traced on.
commit e6dab5ffab59 ("perf/trace: Add ability to set a target task for events") has designed a method to trace these events which specify a target task. But there have tow issues when monitoring multithreaded/multiprocess apps.
First, it match an event(such as wakeup/wakeup_new/stat_*) at the begin, but the function doesn't return, the event will be matched again because of task != current.
Second, due to these events are registered/mmaped at per-cpu or per-thread(--per-thread), so perf_swevent_event will match these events multiple times in the branch(task != current), the number of repetitions is just the number of CPUs or threads.
perf_tp_event will only match an event event at a time, so we will return after an event matched.
Signed-off-by: Cheng Jian <cj.chengjian@huawei.com> --- kernel/events/core.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c index baa134c..5682ead 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -7988,12 +7988,16 @@ void perf_tp_event(u16 event_type, u64 count, void *record, int entry_size, /* Use the given event instead of the hlist */ if (event) { - if (perf_tp_event_match(event, &data, regs)) + if (perf_tp_event_match(event, &data, regs)) { perf_swevent_event(event, count, &data, regs); + goto out; + } } else { hlist_for_each_entry_rcu(event, head, hlist_entry) { - if (perf_tp_event_match(event, &data, regs)) + if (perf_tp_event_match(event, &data, regs)) { perf_swevent_event(event, count, &data, regs); + goto out; + } } } @@ -8015,13 +8019,15 @@ void perf_tp_event(u16 event_type, u64 count, void *record, int entry_size, continue; if (event->attr.config != entry->type) continue; - if (perf_tp_event_match(event, &data, regs)) + if (perf_tp_event_match(event, &data, regs)) { perf_swevent_event(event, count, &data, regs); + break; + } } unlock: rcu_read_unlock(); } - +out: perf_swevent_put_recursion_context(rctx); } EXPORT_SYMBOL_GPL(perf_tp_event); -- 1.8.3.1
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