[PATCH] bfq: Fix computation of shallow depth

[Jan Kara <jack@suse.cz>]

BFQ computes number of tags it allows to be allocated for each request type
based on tag bitmap. However it uses 1 << bitmap.shift as number of
available tags which is wrong. 'shift' is just an internal bitmap value
containing logarithm of how many bits bitmap uses in each bitmap word.
Thus number of tags allowed for some request types can be far to low.
Use proper bitmap.depth which has the number of tags instead.

Signed-off-by: Jan Kara <jack@suse.cz>
---
 block/bfq-iosched.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 9e81d1052091..9e4eb0fc1c16 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -6332,13 +6332,13 @@ static unsigned int bfq_update_depths(struct bfq_data *bfqd,
 	 * limit 'something'.
 	 */
 	/* no more than 50% of tags for async I/O */
-	bfqd->word_depths[0][0] = max((1U << bt->sb.shift) >> 1, 1U);
+	bfqd->word_depths[0][0] = max(bt->sb.depth >> 1, 1U);
 	/*
 	 * no more than 75% of tags for sync writes (25% extra tags
 	 * w.r.t. async I/O, to prevent async I/O from starving sync
 	 * writes)
 	 */
-	bfqd->word_depths[0][1] = max(((1U << bt->sb.shift) * 3) >> 2, 1U);
+	bfqd->word_depths[0][1] = max((bt->sb.depth * 3) >> 2, 1U);
 
 	/*
 	 * In-word depths in case some bfq_queue is being weight-
@@ -6348,9 +6348,9 @@ static unsigned int bfq_update_depths(struct bfq_data *bfqd,
 	 * shortage.
 	 */
 	/* no more than ~18% of tags for async I/O */
-	bfqd->word_depths[1][0] = max(((1U << bt->sb.shift) * 3) >> 4, 1U);
+	bfqd->word_depths[1][0] = max((bt->sb.depth * 3) >> 4, 1U);
 	/* no more than ~37% of tags for sync writes (~20% extra tags) */
-	bfqd->word_depths[1][1] = max(((1U << bt->sb.shift) * 6) >> 4, 1U);
+	bfqd->word_depths[1][1] = max((bt->sb.depth * 6) >> 4, 1U);
 
 	for (i = 0; i < 2; i++)
 		for (j = 0; j < 2; j++)
-- 
2.16.4