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....@arm.com> 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....@arm.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}
