linux-kernel - [patch v2 7/7] blk-mq: add documentation for new queue attribute async

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20251009074634.527661-8-yukuai1@huaweicloud.com>
Date: Thu,  9 Oct 2025 15:46:34 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: axboe@...nel.dk,
	bvanassche@....org,
	ming.lei@...hat.com,
	nilay@...ux.ibm.com,
	jmoyer@...hat.com
Cc: linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	yukuai3@...wei.com,
	yukuai1@...weicloud.com,
	yi.zhang@...wei.com,
	yangerkun@...wei.com,
	johnny.chenyi@...wei.com
Subject: [patch v2 7/7] blk-mq: add documentation for new queue attribute async_dpeth

From: Yu Kuai <yukuai3@...wei.com>

Explain the attribute and the default value in different case.

Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---
 Documentation/ABI/stable/sysfs-block | 34 ++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/Documentation/ABI/stable/sysfs-block b/Documentation/ABI/stable/sysfs-block
index 0ed10aeff86b..aa1e94169666 100644
--- a/Documentation/ABI/stable/sysfs-block
+++ b/Documentation/ABI/stable/sysfs-block
@@ -609,6 +609,40 @@ Description:
 		enabled, and whether tags are shared.
 
 
+What:		/sys/block/<disk>/queue/async_depth
+Date:		August 2025
+Contact:	linux-block@...r.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@....com>
-- 
2.39.2