[PATCH v3 1/2] ubifs: Remove unnecessary cond_resched() from list_sort() compare

[Kuan-Wei Chiu]

Historically, UBIFS embedded cond_resched() calls inside its
list_sort() comparison callbacks (data_nodes_cmp, nondata_nodes_cmp,
and replay_entries_cmp) to prevent soft lockups when sorting long
lists.

However, further inspection by Richard Weinberger reveals that these
compare functions are extremely lightweight and do not perform any
blocking MTD I/O. Furthermore, the lists being sorted are strictly
bounded in size:
- In the GC case, the list contains at most the number of nodes that
  fit into a single LEB.
- In the replay case, the list spans across a few LEBs from the UBIFS
  journal, amounting to at most a few thousand elements.

Since the compare functions are called a few thousand times at most,
the overhead of frequent scheduling points is unjustified. Removing the
cond_resched() calls simplifies the comparison logic and reduces
unnecessary context switch checks during the sort.

Signed-off-by: Kuan-Wei Chiu <visitorckw@xxxxxxxxx>
---
 fs/ubifs/gc.c     | 2 --
 fs/ubifs/replay.c | 1 -
 2 files changed, 3 deletions(-)

diff --git a/fs/ubifs/gc.c b/fs/ubifs/gc.c
index 0bf08b7755b8..933c79b5cd6b 100644
--- a/fs/ubifs/gc.c
+++ b/fs/ubifs/gc.c
@@ -109,7 +109,6 @@ static int data_nodes_cmp(void *priv, const struct list_head *a,
 	struct ubifs_info *c = priv;
 	struct ubifs_scan_node *sa, *sb;
 
-	cond_resched();
 	if (a == b)
 		return 0;
 
@@ -153,7 +152,6 @@ static int nondata_nodes_cmp(void *priv, const struct list_head *a,
 	struct ubifs_info *c = priv;
 	struct ubifs_scan_node *sa, *sb;
 
-	cond_resched();
 	if (a == b)
 		return 0;
 
diff --git a/fs/ubifs/replay.c b/fs/ubifs/replay.c
index a9a568f4a868..263045e05cf1 100644
--- a/fs/ubifs/replay.c
+++ b/fs/ubifs/replay.c
@@ -305,7 +305,6 @@ static int replay_entries_cmp(void *priv, const struct list_head *a,
 	struct ubifs_info *c = priv;
 	struct replay_entry *ra, *rb;
 
-	cond_resched();
 	if (a == b)
 		return 0;
 
-- 
2.53.0.959.g497ff81fa9-goog