Messages in this thread | | | Subject | Re: [PATCH] perf/trace : Fix repetitious traces of perf on tracepoint When i use perf to trace the sched_wakeup_new tracepoint, there is a bug that output the same event repetitiously. It can be reproduced by : | From | "chengjian (D)" <> | Date | Tue, 16 Jan 2018 09:06:16 +0800 |
| |
On 2018/1/15 20:31, Peter Zijlstra wrote:
I'm sorry I gave an inappropriate example to make the phenomenon look confusing.
These events are registered per_cpu and attach in the the perf_event_ctxp of task too. So the same event is placed in the process context CPU times.
perf record -e sched:sched_wakeup_new -vv bug_fork ...... sys_perf_event_open: pid 1063 cpu 0 group_fd -1 flags 0x8 = 4 sys_perf_event_open: pid 1063 cpu 1 group_fd -1 flags 0x8 = 5 sys_perf_event_open: pid 1063 cpu 2 group_fd -1 flags 0x8 = 6 sys_perf_event_open: pid 1063 cpu 3 group_fd -1 flags 0x8 = 8 mmap size 528384B perf event ring buffer mmapped per cpu
/* * If we got specified a target task, also iterate its context and * deliver this event there too. */ // Here we want to see whether this event can be matched by the task not current. // task is the child now.(tracing task) if (task && task != current) { ...... // the event mmaped per cpu, But // task->perf_event_ctxp[perf_sw_context] get all the events attach in this task ctx = rcu_dereference(task->perf_event_ctxp[perf_sw_context]);
list_for_each_entry_rcu(event, &ctx->event_list, event_entry) { if (event->attr.type != PERF_TYPE_TRACEPOINT) continue; if (event->attr.config != entry->type) continue; // event->cpu(3) != task_cpu(1) bug_fork 1063 [003] 128.001255: sched:sched_wakeup_new: comm=bug_fork pid=1064 prio=120 target_cpu=002 // event->cpu(2) != task_cpu(1) bug_fork 1063 [003] 128.001255: sched:sched_wakeup_new: comm=bug_fork pid=1064 prio=120 target_cpu=002 // event->cpu(1) == task_cpu(1) bug_fork 1063 [003] 128.001255: sched:sched_wakeup_new: comm=bug_fork pid=1064 prio=120 target_cpu=002 // event->cpu(0) != task_cpu(1) bug_fork 1063 [003] 128.001255: sched:sched_wakeup_new: comm=bug_fork pid=1064 prio=120 target_cpu=002 // but we only need one about event->cpu(1) == task_cpu(1), the others are repeated if (perf_tp_event_match(event, &data, regs)) perf_swevent_event(event, count, &data, regs); } unlock: rcu_read_unlock(); } ```
>> after this patch, perf script(perf-1039, parent-1040, child-1041): >> >> bug_fork 1040 [002] 36.535963: sched:sched_wakeup_new: >> comm=bug_fork pid=1041 prio=120 target_cpu=003 >> bug_fork 1040 [002] 36.536079: sched:sched_wakeup_new: >> comm=bug_fork pid=1041 prio=120 target_cpu=003 >> >> match it twice, an match for tracing current(parent) and an match >> for task(child). > So what is the bug? The parent gets one, the child gets one, that's > correct, no? > > . So the bug is, we match the same event NR_CPU times when tracing the waken(child process in my demo).
I will modify my commit, and make it clearer.
Thanks.
CHENG Jian
| |