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Subject[PATCH v2 01/10] block, bfq: correctly raise inject limit in bfq_choose_bfqq_for_injection
Date
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@huaweicloud.com>
---
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 a72304c728fc..1220c41fc767 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -4641,12 +4641,10 @@ 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->rq_in_driver < limit) {
+ BFQQ_SECT_THR_NONROT &&
+ bfqd->rq_in_driver >= 1)
+ continue;
+ else {
bfqd->rqs_injected = true;
return bfqq;
}
--
2.30.0
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