Explain the attribute and the default value in different case.
Signed-off-by: Yu Kuai <yukuai@fnnas.com>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.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@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>
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2.51.0