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Message-ID:
<GV1PR08MB105212F94288290E4DD6602DFFB682@GV1PR08MB10521.eurprd08.prod.outlook.com>
Date: Tue, 24 Sep 2024 07:13:31 +0000
From: Yeo Reum Yun <YeoReum.Yun@....com>
To: "rostedt@...dmis.org" <rostedt@...dmis.org>, "mhiramat@...nel.org"
<mhiramat@...nel.org>, "mathieu.desnoyers@...icios.com"
<mathieu.desnoyers@...icios.com>, "a.p.zijlstra@...llo.nl"
<a.p.zijlstra@...llo.nl>, "mingo@...e.hu" <mingo@...e.hu>, Mark Rutland
<Mark.Rutland@....com>, "james.clark@...aro.org" <james.clark@...aro.org>
CC: nd <nd@....com>, "linux-kernel@...r.kernel.org"
<linux-kernel@...r.kernel.org>, "linux-trace-kernel@...r.kernel.org"
<linux-trace-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] trace/trace_event_perf: remove duplicate samples on
the first tracepoint event
Gentle ping
________________________________________
From: Levi Yun <yeoreum.yun@....com>
Sent: 13 September 2024 03:13
To: rostedt@...dmis.org; mhiramat@...nel.org; mathieu.desnoyers@...icios.com; a.p.zijlstra@...llo.nl; mingo@...e.hu; Mark Rutland; james.clark@...aro.org
Cc: nd; linux-kernel@...r.kernel.org; linux-trace-kernel@...r.kernel.org; Yeo Reum Yun
Subject: [PATCH v2] trace/trace_event_perf: remove duplicate samples on the first tracepoint event
When a tracepoint event is created with attr.freq = 1,
'hwc->period_left' is not initialized correctly. As a result,
in the perf_swevent_overflow() function, when the first time the event occurs,
it calculates the event overflow and the perf_swevent_set_period() returns 3,
this leads to the event are recorded for three duplicate times.
Step to reproduce:
1. Enable the tracepoint event & starting tracing
$ echo 1 > /sys/kernel/tracing/events/module/module_free
$ echo 1 > /sys/kernel/tracing/tracing_on
2. Record with perf
$ perf record -a --strict-freq -F 1 -e "module:module_free"
3. Trigger module_free event.
$ modprobe -i sunrpc
$ modprobe -r sunrpc
Result:
- Trace pipe result:
$ cat trace_pipe
modprobe-174509 [003] ..... 6504.868896: module_free: sunrpc
- perf sample:
modprobe 174509 [003] 6504.868980: module:module_free: sunrpc
modprobe 174509 [003] 6504.868980: module:module_free: sunrpc
modprobe 174509 [003] 6504.868980: module:module_free: sunrpc
By setting period_left via perf_swevent_set_period() as other sw_event did,
This problem could be solved.
After patch:
- Trace pipe result:
$ cat trace_pipe
modprobe 1153096 [068] 613468.867774: module:module_free: xfs
- perf sample
modprobe 1153096 [068] 613468.867794: module:module_free: xfs
Fixes: bd2b5b12849a ("perf_counter: More aggressive frequency adjustment")
Signed-off-by: Levi Yun <yeoreum.yun@....com>
---
Changes in v2:
- Fix build error.
---
kernel/trace/trace_event_perf.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index 05e791241812..3ff9caa4a71b 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -352,10 +352,16 @@ void perf_uprobe_destroy(struct perf_event *p_event)
int perf_trace_add(struct perf_event *p_event, int flags)
{
struct trace_event_call *tp_event = p_event->tp_event;
+ struct hw_perf_event *hwc = &p_event->hw;
if (!(flags & PERF_EF_START))
p_event->hw.state = PERF_HES_STOPPED;
+ if (is_sampling_event(p_event)) {
+ hwc->last_period = hwc->sample_period;
+ perf_swevent_set_period(p_event);
+ }
+
/*
* If TRACE_REG_PERF_ADD returns false; no custom action was performed
* and we need to take the default action of enqueueing our event on
--
LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}
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