[PATCH BUGFIX RFC 1/2] Revert "bfq-iosched: remove unused variable"

[Paolo Valente <paolo.valente@linaro.org>]

This reverts commit bd7d4ef6a4c9b3611fa487a0065bf042c71ce620.
---
 block/bfq-iosched.c | 15 ++++++++-------
 block/bfq-iosched.h |  6 ++++++
 2 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index cd307767a134..8cc3032b66de 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -5303,25 +5303,26 @@ static unsigned int bfq_update_depths(struct bfq_data *bfqd,
 				      struct sbitmap_queue *bt)
 {
 	unsigned int i, j, min_shallow = UINT_MAX;
+	bfqd->sb_shift = bt->sb.shift;
 
 	/*
 	 * In-word depths if no bfq_queue is being weight-raised:
 	 * leaving 25% of tags only for sync reads.
 	 *
 	 * In next formulas, right-shift the value
-	 * (1U<<bt->sb.shift), instead of computing directly
-	 * (1U<<(bt->sb.shift - something)), to be robust against
-	 * any possible value of bt->sb.shift, without having to
+	 * (1U<<bfqd->sb_shift), instead of computing directly
+	 * (1U<<(bfqd->sb_shift - something)), to be robust against
+	 * any possible value of bfqd->sb_shift, without having to
 	 * 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((1U<<bfqd->sb_shift)>>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(((1U<<bfqd->sb_shift) * 3)>>2, 1U);
 
 	/*
 	 * In-word depths in case some bfq_queue is being weight-
@@ -5331,9 +5332,9 @@ 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(((1U<<bfqd->sb_shift) * 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(((1U<<bfqd->sb_shift) * 6)>>4, 1U);
 
 	for (i = 0; i < 2; i++)
 		for (j = 0; j < 2; j++)
diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
index 0b02bf302de0..4de5dc349a1e 100644
--- a/block/bfq-iosched.h
+++ b/block/bfq-iosched.h
@@ -697,6 +697,12 @@ struct bfq_data {
 	/* bfqq associated with the task issuing current bio for merging */
 	struct bfq_queue *bio_bfqq;
 
+	/*
+	 * Cached sbitmap shift, used to compute depth limits in
+	 * bfq_update_depths.
+	 */
+	unsigned int sb_shift;
+
 	/*
 	 * Depth limits used in bfq_limit_depth (see comments on the
 	 * function)
-- 
2.20.1