Re: [PATCH] tracing: kprobe-event: Return directly when dyn_event_list is empty
On Mon, 26 Jan 2026 15:17:28 +0800 sunliming wrote: > Alternatively, could both optimization solutions coexist (as lock > contention may Yes, the two are orthogonal to each other, and can go in on their own merit. -- Steve
Re: [PATCH] tracing: kprobe-event: Return directly when dyn_event_list is empty
On Mon, 26 Jan 2026 10:56:59 +0800 sunliming wrote: > During kernel boot, the setup_boot_kprobe_events() function causes > significant delays, increasing overall startup time. > > The root cause is a lock contention chain: its child function > > enable_boot_kprobe_events() requires the event_mutex, which is already > > held by early_event_add_tracer(). early_event_add_tracer() itself is > blocked Ah, early_event_add_tracer() is called by the work function that sets up tracers (and the event directories within them). > > waiting for the trace_event_sem read-write lock, which is held for an > extended > > period by trace_event_update_all(). trace_event_update_all() is > runing in > > eval_map_work_func() in eval_map_wq. > > On my ARM64 platform machine, the latency can reach around 200ms： > > [ 0.268848] trace_kprobe: try_get_event_mutex > kernel/trace/tracekprobe.c,1902,enable_boot_kprobe_events > [ 0.268849] try down_write > kernel/trace/traceevents.c,4114,early_event_add_tracer > [ 0.482382] done up_write > kernel/trace/trace_events.c,3074,trace_event_eval_update > [ 0.482386] done down_write > kernel/trace/trace_events.c,4116,early_event_add_tracer > [ 0.482868] done up_write > kernel/trace/trace_events.c,4119,early_event_add_tracer > [ 0.482877] trace_kprobe: enable_boot_kprobe_events geted eventmutex > [ 0.482879] trace_kprobe: enable_bootk_probe_events release eventmutex I take it that you are aware of this work, as it comes from someone with the same email domain as you have. https://lore.kernel.org/all/[email protected]/ That is moving the kprobe setup into the same work function. -- Steve
Re: [PATCH] tracing: kprobe-event: Return directly when dyn_event_list is empty
On Fri, 23 Jan 2026 09:36:41 +0800 [email protected] wrote: > From: sunliming > > In enable_boot_kprobe_events(), it returns directly when dyn_event_list is > empty, thereby reducing the function's execution time. This function may > otherwise wait for the event_mutex lock for tens of milliseconds on certain > machines, which is unnecessary when dyn_event_list is empty. Have you measured this? I'm curious as to what may be holding the event_mutex at this time. This is called by the initcall functions which are currently all serialized. Any conflict would have to be caused by a worker or kthread and not another initcall callback. I'm not against the patch, I just want to understand more about it. > > Signed-off-by: sunliming > --- > kernel/trace/trace_kprobe.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c > index 9953506370a5..d89a403c99d4 100644 > --- a/kernel/trace/trace_kprobe.c > +++ b/kernel/trace/trace_kprobe.c > @@ -1982,6 +1982,9 @@ static __init void enable_boot_kprobe_events(void) > struct trace_kprobe *tk; > struct dyn_event *pos; > > + if (list_empty(&dyn_event_list)) > + return; The above should definitely have a comment or we should wrap that with another macro because the above is assuming that for_each_trace_kprobe() uses dyn_event_list. If that ever changes in the future, this will be broken. Perhaps we should add a: if (trace_kprobe_list_empty()) return; ? -- Steve > + > guard(mutex)(&event_mutex); > for_each_trace_kprobe(tk, pos) { > list_for_each_entry(file, &tr->events, list)
[PATCH] tracing: kprobe-event: Return directly when dyn_event_list is empty
From: sunliming
In enable_boot_kprobe_events(), it returns directly when dyn_event_list is
empty, thereby reducing the function's execution time. This function may
otherwise wait for the event_mutex lock for tens of milliseconds on certain
machines, which is unnecessary when dyn_event_list is empty.
Signed-off-by: sunliming
---
kernel/trace/trace_kprobe.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 9953506370a5..d89a403c99d4 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -1982,6 +1982,9 @@ static __init void enable_boot_kprobe_events(void)
struct trace_kprobe *tk;
struct dyn_event *pos;
+ if (list_empty(&dyn_event_list))
+ return;
+
guard(mutex)(&event_mutex);
for_each_trace_kprobe(tk, pos) {
list_for_each_entry(file, &tr->events, list)
--
2.25.1
