[PATCH] sbitmap: don't loop for find_next_zero_bit() for !round_robin

[Jens Axboe <axboe@kernel.dk>]

If we aren't forced to do round robin tag allocation, just use the
allocation hint to find the index for the tag word, don't use it for the
offset inside the word. This avoids a potential extra round trip in the
bit looping.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

---

diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index fdd1b8aa8ac6..2987b2ac8ed7 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -118,10 +118,19 @@ int sbitmap_get(struct sbitmap *sb, unsigned int alloc_hint, bool round_robin)
 
 	index = SB_NR_TO_INDEX(sb, alloc_hint);
 
+	/*
+	 * Unless we're doing round robin tag allocation, just use the
+	 * alloc_hint to find the right word index. No point in looping
+	 * twice in find_next_zero_bit() for that case.
+	 */
+	if (round_robin)
+		alloc_hint = SB_NR_TO_BIT(sb, alloc_hint);
+	else
+		alloc_hint = 0;
+
 	for (i = 0; i < sb->map_nr; i++) {
 		nr = __sbitmap_get_word(&sb->map[index].word,
-					sb->map[index].depth,
-					SB_NR_TO_BIT(sb, alloc_hint),
+					sb->map[index].depth, alloc_hint,
 					!round_robin);
 		if (nr != -1) {
 			nr += index << sb->shift;
@@ -130,12 +139,8 @@ int sbitmap_get(struct sbitmap *sb, unsigned int alloc_hint, bool round_robin)
 
 		/* Jump to next index. */
 		index++;
-		alloc_hint = index << sb->shift;
-
-		if (index >= sb->map_nr) {
+		if (index >= sb->map_nr)
 			index = 0;
-			alloc_hint = 0;
-		}
 	}
 
 	return nr;

-- 
Jens Axboe