From: Yu Kuai Date: Tue, 3 Feb 2026 08:19:49 +0000 (+0800) Subject: blk-mq: add documentation for new queue attribute async_dpeth X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2c04718edcd5e1ac8fed9a0f8d0620e8bc94014d;p=thirdparty%2Flinux.git blk-mq: add documentation for new queue attribute async_dpeth Explain the attribute and the default value in different case. Signed-off-by: Yu Kuai Reviewed-by: Nilay Shroff Signed-off-by: Jens Axboe --- diff --git a/Documentation/ABI/stable/sysfs-block b/Documentation/ABI/stable/sysfs-block index 0ed10aeff86b8..aa1e94169666b 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//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//queue/nr_zones Date: November 2018 Contact: Damien Le Moal