Commit 10825410 authored by Laibin Qiu's avatar Laibin Qiu Committed by Jens Axboe
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blk-mq: Fix wrong wakeup batch configuration which will cause hang 

Commit 180dccb0 ("blk-mq: fix tag_get wait task can't be
awakened") will recalculate wake_batch when incrementing or decrementing
active_queues to avoid wake_batch > hctx_max_depth. At the same time, in
order to not affect performance as much as possible, the minimum wakeup
batch is set to 4. But when the QD is small (such as QD=1), if inc or dec
active_queues increases wakeup batch, that can lead to a hang:

Fix this problem with the following strategies:
QD          :  >= 32 | < 32
---------------------------------
wakeup batch:  8~4   | 3~1

Fixes: 180dccb0 ("blk-mq: fix tag_get wait task can't be awakened")
Link: https://lore.kernel.org/linux-block/78cafe94-a787-e006-8851-69906f0c2128@huawei.com/T/#t


Reported-by: default avatarAlex Xu (Hello71) <alex_y_xu@yahoo.ca>
Signed-off-by: default avatarLaibin Qiu <qiulaibin@huawei.com>
Tested-by: default avatarAlex Xu (Hello71) <alex_y_xu@yahoo.ca>
Link: https://lore.kernel.org/r/20220127100047.1763746-1-qiulaibin@huawei.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 3c8cef9f

lib/sbitmap.c

+6 −2
Original line number Diff line number Diff line
@@ -488,9 +488,13 @@ void sbitmap_queue_recalculate_wake_batch(struct sbitmap_queue *sbq, 
					    unsigned int users)

{

	unsigned int wake_batch;

	unsigned int min_batch;

	unsigned int depth = (sbq->sb.depth + users - 1) / users;



	wake_batch = clamp_val((sbq->sb.depth + users - 1) /

			users, 4, SBQ_WAKE_BATCH);

	min_batch = sbq->sb.depth >= (4 * SBQ_WAIT_QUEUES) ? 4 : 1;



	wake_batch = clamp_val(depth / SBQ_WAIT_QUEUES,

			min_batch, SBQ_WAKE_BATCH);

	__sbitmap_queue_update_wake_batch(sbq, wake_batch);

}

EXPORT_SYMBOL_GPL(sbitmap_queue_recalculate_wake_batch);