linux-kernel - [PATCH 1/2] perf: Introduce default_overflow

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Message-ID: <176179482721.959775.9568162681903659824.stgit@devnote2>
Date: Thu, 30 Oct 2025 12:27:07 +0900
From: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>
Cc: Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	Will Deacon <will@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	linux-arm-kernel@...ts.infradead.org
Subject: [PATCH 1/2] perf: Introduce default_overflow_compatible flag

From: Masami Hiramatsu (Google) <mhiramat@...nel.org>

Instead of checking whether event->overflow_handler everytime in
is_default_overflow_handler(), just use a flag to check it once when
registering the handler.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
---
 include/linux/perf_event.h |    9 ++-------
 kernel/events/core.c       |    2 ++
 2 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index fd1d91017b99..40dd897e26b0 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -902,6 +902,7 @@ struct perf_event {
 	u64				(*clock)(void);
 	perf_overflow_handler_t		overflow_handler;
 	void				*overflow_handler_context;
+	bool				default_overflow_compatible;
 	struct bpf_prog			*prog;
 	u64				bpf_cookie;
 
@@ -1505,13 +1506,7 @@ extern int perf_event_output(struct perf_event *event,
 static inline bool
 is_default_overflow_handler(struct perf_event *event)
 {
-	perf_overflow_handler_t overflow_handler = event->overflow_handler;
-
-	if (likely(overflow_handler == perf_event_output_forward))
-		return true;
-	if (unlikely(overflow_handler == perf_event_output_backward))
-		return true;
-	return false;
+	return event->default_overflow_compatible;
 }
 
 extern void
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 177e57c1a362..6bbbde82cb21 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -12946,9 +12946,11 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
 	} else if (is_write_backward(event)){
 		event->overflow_handler = perf_event_output_backward;
 		event->overflow_handler_context = NULL;
+		event->default_overflow_compatible = true;
 	} else {
 		event->overflow_handler = perf_event_output_forward;
 		event->overflow_handler_context = NULL;
+		event->default_overflow_compatible = true;
 	}
 
 	perf_event__state_init(event);