linux-kernel - [PATCH] perf/HWBP: Optimize __modify_bp

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Message-ID: <20250902091759.590664-1-wangjinchao600@gmail.com>
Date: Tue,  2 Sep 2025 17:17:54 +0800
From: Jinchao Wang <wangjinchao600@...il.com>
To: Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	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>,
	"Liang, Kan" <kan.liang@...ux.intel.com>,
	linux-perf-users@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	Jinchao Wang <wangjinchao600@...il.com>
Subject: [PATCH] perf/HWBP: Optimize __modify_bp_slot() handling

Skip unnecessary release/reserve when old and new types share the same
slot.

Reserve the new slot first, then release the old one to maintain
consistency and avoid transient failures.

Signed-off-by: Jinchao Wang <wangjinchao600@...il.com>
---
 kernel/events/hw_breakpoint.c | 23 ++++++++++-------------
 1 file changed, 10 insertions(+), 13 deletions(-)

diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
index 8ec2cb688903..1cc9cb32ceb4 100644
--- a/kernel/events/hw_breakpoint.c
+++ b/kernel/events/hw_breakpoint.c
@@ -625,23 +625,20 @@ void release_bp_slot(struct perf_event *bp)
 static int __modify_bp_slot(struct perf_event *bp, u64 old_type, u64 new_type)
 {
 	int err;
+	enum bp_type_idx old_type_idx, new_type_idx;
 
-	__release_bp_slot(bp, old_type);
+	old_type_idx = find_slot_idx(old_type);
+	new_type_idx = find_slot_idx(new_type);
+	if (old_type_idx == new_type_idx)
+		return 0;
 
 	err = __reserve_bp_slot(bp, new_type);
-	if (err) {
-		/*
-		 * Reserve the old_type slot back in case
-		 * there's no space for the new type.
-		 *
-		 * This must succeed, because we just released
-		 * the old_type slot in the __release_bp_slot
-		 * call above. If not, something is broken.
-		 */
-		WARN_ON(__reserve_bp_slot(bp, old_type));
-	}
+	if (err)
+		return err;
 
-	return err;
+	__release_bp_slot(bp, old_type);
+
+	return 0;
 }
 
 static int modify_bp_slot(struct perf_event *bp, u64 old_type, u64 new_type)
-- 
2.43.0