Gentle ping in case of forgotten. ________________________________________ From: Steven Rostedt <[email protected]> Sent: 26 September 2024 13:51 To: Yeo Reum Yun Cc: [email protected]; [email protected]; [email protected]; [email protected]; Mark Rutland; [email protected]; nd; [email protected]; [email protected]; Peter Zijlstra; Frederic Weisbecker; Arnaldo Carvalho de Melo; Namhyung Kim Subject: Re: [PATCH v2] trace/trace_event_perf: remove duplicate samples on the first tracepoint event
Can one of the perf folks give me an Ack, and I'll take this through my tree. -- Steve On Fri, 13 Sep 2024 03:13:47 +0100 Levi Yun <[email protected]> wrote: > 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 <[email protected]> > --- > 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}
