linux-kernel - [PATCH 1/3] locking/lockdep: unlikely bfs

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Date:   Thu, 17 Jun 2021 22:28:26 +0800
From:   Xiongwei Song <sxwjean@...com>
To:     peterz@...radead.org, mingo@...hat.com, will@...nel.org,
        longman@...hat.com, boqun.feng@...il.com
Cc:     linux-kernel@...r.kernel.org, Xiongwei Song <sxwjean@...il.com>
Subject: [PATCH 1/3] locking/lockdep: unlikely bfs_error() inside

From: Xiongwei Song <sxwjean@...il.com>

The error from graph walk is small probability event, and there are some
bfs_error calls during lockdep detection, so unlikely bfs_error inside
can improve performance a little bit.

Suggested-by: Waiman Long <longman@...hat.com>
Signed-off-by: Xiongwei Song <sxwjean@...il.com>
---
 kernel/locking/lockdep.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 7641bd407239..a8a66a2a9bc1 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1540,7 +1540,7 @@ enum bfs_result {
  */
 static inline bool bfs_error(enum bfs_result res)
 {
-	return res < 0;
+	return unlikely(res < 0);
 }
 
 /*
@@ -2089,7 +2089,7 @@ check_path(struct held_lock *target, struct lock_list *src_entry,
 
 	ret = __bfs_forwards(src_entry, target, match, skip, target_entry);
 
-	if (unlikely(bfs_error(ret)))
+	if (bfs_error(ret))
 		print_bfs_bug(ret);
 
 	return ret;
@@ -2936,7 +2936,7 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
 	 * in the graph whose neighbours are to be checked.
 	 */
 	ret = check_noncircular(next, prev, trace);
-	if (unlikely(bfs_error(ret) || ret == BFS_RMATCH))
+	if (bfs_error(ret) || unlikely(ret == BFS_RMATCH))
 		return 0;
 
 	if (!check_irq_usage(curr, prev, next))
-- 
2.30.2