linux-kernel - [PATCH v3] perf/trace : Fix repetitious traces of perf on tracepoint

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Date:   Tue, 16 Jan 2018 20:40:38 +0800
From:   Cheng Jian <cj.chengjian@...wei.com>
To:     <peterz@...radead.org>, <mingo@...hat.com>, <acme@...nel.org>,
        <alexander.shishkin@...ux.intel.com>, <jolsa@...hat.com>,
        <namhyung@...nel.org>, <xiexiuqi@...wei.com>,
        <huawei.libin@...wei.com>, <wangnan0@...wei.com>
CC:     <cj.chengjian@...wei.com>, <linux-kernel@...r.kernel.org>
Subject: [PATCH v3] 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 :

	#./test_fork
		parent pid : 1059
		child pid : 1060
	#perf record -e sched:sched_wakeup_new -p 1060

test_fork is an demo that can generating wakeup_new event, parent
process does nothing but fork a child process, and then they both
quit.

There are 4 processors in this machine. before this patch,
perf script(perf-1058, parent-1059, child-1060) :

        test_fork  1059 [001]    62.913689: sched:sched_wakeup_new: comm=test_fork pid=1060 prio=120 target_cpu=002
        test_fork  1059 [001]    62.913698: sched:sched_wakeup_new: comm=test_fork pid=1060 prio=120 target_cpu=002
        test_fork  1059 [001]    62.913705: sched:sched_wakeup_new: comm=test_fork pid=1060 prio=120 target_cpu=002

but ftrace report this event only once :

	test_fork-1059  [002] d...   62.913680: sched_wakeup_new: comm=test_fork pid=1060 prio=120 target_cpu=002

perf script print the same wakeup_new event multiple times.

These events which trigger this issue all specify a target process.
commit e6dab5ffab59 ("perf/trace: Add ability to set a target task
for events") has designed a method to trace these events. For
example, the sched_wakeup and sched_wakeup_new tracepoint will be
caught when the current task wakeup a target task.

These events are registered as per cpu most of the time and attached
to the task too, we will get all of them from the perf_event_context
of this task, they will be matched success but are all the same event.
So check the cpu number of this event to avoid matching them multiple
times.

after this patch, perf script(parent-1040, child-1041):

	test_fork  1040 [002]    36.536079: sched:sched_wakeup_new: comm=test_fork pid=1041 prio=120 target_cpu=003

It will match it only once for tracing task(child-1041).

Signed-off-by: Cheng Jian <cj.chengjian@...wei.com>
---
 kernel/events/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 4df5b69..a199c03 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7924,6 +7924,8 @@ void perf_tp_event(u16 event_type, u64 count, void *record, int entry_size,
 				continue;
 			if (event->attr.config != entry->type)
 				continue;
+			if (event->cpu != task_cpu(task) && event->cpu != -1)
+				continue;
 			if (perf_tp_event_match(event, &data, regs))
 				perf_swevent_event(event, count, &data, regs);
 		}
-- 
1.8.3.1