linux-kernel - [PATCH] kcmp: improve performance adding an unlikely hint to task comparisons

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Message-ID: <20250213163916.709392-1-colin.i.king@gmail.com>
Date: Thu, 13 Feb 2025 16:39:16 +0000
From: Colin Ian King <colin.i.king@...il.com>
To: Christian Brauner <brauner@...nel.org>,
	Al Viro <viro@...iv.linux.org.uk>
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH] kcmp: improve performance adding an unlikely hint to task comparisons

Adding an unlikely() hint on task comparisons on an unlikely error
return path improves run-time performance of the kcmp system call.

Benchmarking on an i9-12900 shows an improvement of ~5.5% on kcmp().
Results based on running 20 tests with turbo disabled (to reduce
clock freq turbo changes), with 10 second run per test and comparing
the number of kcmp calls per second. The % Standard deviation of 20
tests was ~0.25%, results are reliable.

Signed-off-by: Colin Ian King <colin.i.king@...il.com>
---
 kernel/kcmp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/kcmp.c b/kernel/kcmp.c
index 2c596851f8a9..7c1a65bd5f8d 100644
--- a/kernel/kcmp.c
+++ b/kernel/kcmp.c
@@ -145,7 +145,7 @@ SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type,
 	 */
 	task1 = find_task_by_vpid(pid1);
 	task2 = find_task_by_vpid(pid2);
-	if (!task1 || !task2)
+	if (unlikely(!task1 || !task2))
 		goto err_no_task;

 	get_task_struct(task1);
-- 
2.47.2