linux-kernel - [PATCH v4 1/8] block, bfq: correctly raise inject limit in bfq_choose_bfqq_for

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Message-Id: <20230116095153.3810101-2-shikemeng@huaweicloud.com>
Date:   Mon, 16 Jan 2023 17:51:46 +0800
From:   Kemeng Shi <shikemeng@...weicloud.com>
To:     jack@...e.com, damien.lemoal@...nsource.wdc.com,
        paolo.valente@...aro.org, axboe@...nel.dk
Cc:     hch@....de, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v4 1/8] block, bfq: correctly raise inject limit in bfq_choose_bfqq_for_injection

Function bfq_choose_bfqq_for_injection may temporarily raise inject limit
to one request if current inject_limit is 0 before search of the source
queue for injection. However the search below will reset inject limit to
bfqd->in_service_queue which is zero for raised inject limit. Then the
temporarily raised inject limit never works as expected.
Assigment limit to bfqd->in_service_queue in search is needed as limit
maybe overwriten to min_t(unsigned int, 1, limit) for condition that
a large in-flight request is on non-rotational devices in found queue.
So we need to reset limit to bfqd->in_service_queue for normal case.

Actually, we have already make sure bfqd->rq_in_driver is < limit before
search, then
 -Limit is >= 1 as bfqd->rq_in_driver is >= 0. Then min_t(unsigned int,
1, limit) is always 1. So we can simply check bfqd->rq_in_driver with
1 instead of result of min_t(unsigned int, 1, limit) for larget request in
non-rotational device case to avoid overwritting limit and the bug is gone.
 -For normal case, we have already check bfqd->rq_in_driver is < limit,
so we can return found bfqq unconditionally to remove unncessary check.

Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>
Reviewed-by: Jan Kara <jack@...e.cz>
---
 block/bfq-iosched.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 815b884d6c5a..8836221a2673 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -4730,12 +4730,10 @@ bfq_choose_bfqq_for_injection(struct bfq_data *bfqd)
 			 */
 			if (blk_queue_nonrot(bfqd->queue) &&
 			    blk_rq_sectors(bfqq->next_rq) >=
-			    BFQQ_SECT_THR_NONROT)
-				limit = min_t(unsigned int, 1, limit);
-			else
-				limit = in_serv_bfqq->inject_limit;
-
-			if (bfqd->tot_rq_in_driver < limit) {
+			    BFQQ_SECT_THR_NONROT &&
+			    bfqd->tot_rq_in_driver >= 1)
+				continue;
+			else {
 				bfqd->rqs_injected = true;
 				return bfqq;
 			}
-- 
2.30.0