This is a note to let you know that I've just added the patch titled bfq-iosched: Revert "bfq: Fix computation of shallow depth" to the 5.10-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: bfq-iosched-revert-bfq-fix-computation-of-shallow-de.patch and it can be found in the queue-5.10 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 5b07d26ffa2e6bced341949c4f4c37c3815eb8d4 Author: Lin Feng <linf@xxxxxxxxxx> Date: Tue Feb 2 07:18:23 2021 -0700 bfq-iosched: Revert "bfq: Fix computation of shallow depth" [ Upstream commit 388c705b95f23f317fa43e6abf9ff07b583b721a ] 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@xxxxxxxxxx> Reviewed-by: Jan Kara <jack@xxxxxxx> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 9e4eb0fc1c16e..9e81d1052091f 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(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++)