bfq-iosched: Revert "bfq: Fix computation of shallow depth"

This reverts commit 6d4d273588378c65915acaf7b2ee74e9dd9c130a.

bfq.limit_depth passes word_depths[] as shallow_depth down to sbitmap core
sbitmap_get_shallow, which uses just the number to limit the scan depth of
each bitmap word, formula:
scan_percentage_for_each_word = shallow_depth / (1 << sbimap->shift) * 100%

That means the comments's percentiles 50%, 75%, 18%, 37% of bfq are correct.
But after commit patch 'bfq: Fix computation of shallow depth', we use
sbitmap.depth instead, as a example in following case:

sbitmap.depth = 256, map_nr = 4, shift = 6; sbitmap_word.depth = 64.
The resulsts of computed bfqd->word_depths[] are {128, 192, 48, 96}, and
three of the numbers exceed core dirver's 'sbitmap_word.depth=64' limit
nothing.

Signed-off-by: Lin Feng <linf@wangsu.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 9e4eb0f..9e81d10 100644 (file)
--- 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(bt->sb.depth >> 1, 1U);
+       bfqd->word_depths[0][0] = max((1U << bt->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((bt->sb.depth * 3) >> 2, 1U);
+       bfqd->word_depths[0][1] = max(((1U << bt->sb.shift) * 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((bt->sb.depth * 3) >> 4, 1U);
+       bfqd->word_depths[1][0] = max(((1U << bt->sb.shift) * 3) >> 4, 1U);
        /* no more than ~37% of tags for sync writes (~20% extra tags) */
-       bfqd->word_depths[1][1] = max((bt->sb.depth * 6) >> 4, 1U);
+       bfqd->word_depths[1][1] = max(((1U << bt->sb.shift) * 6) >> 4, 1U);
 
        for (i = 0; i < 2; i++)
                for (j = 0; j < 2; j++)