Commit 388c705b authored by Lin Feng's avatar Lin Feng Committed by Jens Axboe
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bfq-iosched: Revert "bfq: Fix computation of shallow depth" 



This reverts commit 6d4d2735.

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: default avatarLin Feng <linf@wangsu.com>
Reviewed-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent cd92cdb9

block/bfq-iosched.c

+4 −4
Original line number Diff line number Diff line
@@ -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++)