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authorLin Feng <linf@wangsu.com>2021-02-02 07:18:23 -0700
committerJens Axboe <axboe@kernel.dk>2021-02-02 20:37:08 -0700
commit388c705b95f23f317fa43e6abf9ff07b583b721a (patch)
tree1675ad44ead9a496c2918b0f21de433037c0f1e4
parentcd92cdb9c8bcfc27a8f28bcbf7c414a0ea79e5ec (diff)
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>
-rw-r--r--block/bfq-iosched.c8
1 files changed, 4 insertions, 4 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 9e4eb0fc1c16..9e81d1052091 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++)