Re: [PATCH v2] trace/trace_event_perf: remove duplicate samples on the first tracepoint event

[Yeo Reum Yun]

Gentle ping in case of forgotten.

________________________________________
From: Steven Rostedt <rostedt@xxxxxxxxxxx>
Sent: 26 September 2024 13:51
To: Yeo Reum Yun
Cc: mhiramat@xxxxxxxxxx; mathieu.desnoyers@xxxxxxxxxxxx; a.p.zijlstra@xxxxxxxxx; mingo@xxxxxxx; Mark Rutland; james.clark@xxxxxxxxxx; nd; linux-kernel@xxxxxxxxxxxxxxx; linux-trace-kernel@xxxxxxxxxxxxxxx; 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 <yeoreum.yun@xxxxxxx> 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 <yeoreum.yun@xxxxxxx>
> ---
> 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}