linux-kernel - [PATCH v2] perf/trace : Fix repetitious traces of perf on tracepoint

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Message-ID: <1516019804-6908-1-git-send-email-cj.chengjian@huawei.com>
Date:   Mon, 15 Jan 2018 20:36:44 +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 v2] 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 :

	perf record -e sched:sched_wakeup_new ./bug_fork

bug_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) :

	bug_fork  1059 [001]    62.913666: sched:sched_wakeup_new:
comm=bug_fork pid=1060 prio=120 target_cpu=002
        bug_fork  1059 [001]    62.913680: sched:sched_wakeup_new:
comm=bug_fork pid=1060 prio=120 target_cpu=002
        bug_fork  1059 [001]    62.913689: sched:sched_wakeup_new:
comm=bug_fork pid=1060 prio=120 target_cpu=002
        bug_fork  1059 [001]    62.913698: sched:sched_wakeup_new:
comm=bug_fork pid=1060 prio=120 target_cpu=002
        bug_fork  1059 [001]    62.913705: sched:sched_wakeup_new:
comm=bug_fork pid=1060 prio=120 target_cpu=002

but ftrace report this event only once :

	bug_fork-1059  [002] d...   62.913666: sched_wakeup_new:
comm=bug_fork pid=1060 prio=120 target_cpu=002

perf script print 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. If we trace both
of them and task(waken) != current(wakee), it will match this event
at the beginning for tracing current task, and then match again for
tracing the waken task. But these events are registered at all cpus
most of the time, so these events will be matched nr_cpu times
in this branch.

We just forcus on the task thread here, so check the cpu number of
this event and task.

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).

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