Commit 2c04718e authored by Yu Kuai's avatar Yu Kuai Committed by Jens Axboe
Browse files

blk-mq: add documentation for new queue attribute async_dpeth 



Explain the attribute and the default value in different case.

Signed-off-by: default avatarYu Kuai <yukuai@fnnas.com>
Reviewed-by: default avatarNilay Shroff <nilay@linux.ibm.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 2110858c

Documentation/ABI/stable/sysfs-block

+34 −0
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@@ -609,6 +609,40 @@ Description: 
		enabled, and whether tags are shared.





What:		/sys/block/<disk>/queue/async_depth

Date:		August 2025

Contact:	linux-block@vger.kernel.org

Description:

		[RW] Controls how many asynchronous requests may be allocated in the

		block layer. The value is always capped at nr_requests.



		When no elevator is active (none):

		- async_depth is always equal to nr_requests.



		For bfq scheduler:

		- By default, async_depth is set to 75% of nr_requests.

		  Internal limits are then derived from this value:

		  * Sync writes: limited to async_depth (≈75% of nr_requests).

		  * Async I/O: limited to ~2/3 of async_depth (≈50% of nr_requests).



		  If a bfq_queue is weight-raised:

		  * Sync writes: limited to ~1/2 of async_depth (≈37% of nr_requests).

		  * Async I/O: limited to ~1/4 of async_depth (≈18% of nr_requests).



		- If the user writes a custom value to async_depth, BFQ will recompute

		  these limits proportionally based on the new value.



		For Kyber:

		- By default async_depth is set to 75% of nr_requests.

		- If the user writes a custom value to async_depth, then it override the

		  default and directly control the limit for writes and async I/O.



		For mq-deadline:

		- By default async_depth is set to nr_requests.

		- If the user writes a custom value to async_depth, then it override the

		  default and directly control the limit for writes and async I/O.





What:		/sys/block/<disk>/queue/nr_zones

Date:		November 2018

Contact:	Damien Le Moal <damien.lemoal@wdc.com>