Document a new Btrfs mount option, wq_cpu_set.
Signed-off-by: Ammar Faizi <ammarfaizi2@xxxxxxxxxxx>
---
Documentation/ch-mount-options.rst | 29 +++++++++++++++++++++++++++++
1 file changed, 29 insertions(+)
diff --git a/Documentation/ch-mount-options.rst b/Documentation/ch-mount-options.rst
index f0f205dc20fa15ff..48fe63ee5e95c297 100644
--- a/Documentation/ch-mount-options.rst
+++ b/Documentation/ch-mount-options.rst
@@ -451,6 +451,35 @@ user_subvol_rm_allowed
ordinary directory. Whether this is possible can be detected at runtime, see
*rmdir_subvol* feature in *FILESYSTEM FEATURES*.
+wq_cpu_set=<cpu_set>
+ (since: 6.5, default: all online CPUs)
+
+ Btrfs workqueues can slow sensitive user tasks down because they can use any
+ online CPU to perform heavy workloads on an SMP system. This option is used to
+ isolate the Btrfs workqueues to a set of CPUs. It is helpful to avoid
+ sensitive user tasks being preempted by Btrfs heavy workqueues.
+
+ The *cpu_set* is a dot-separated list of decimal numbers and ranges. The
+ numbers are CPU numbers, the ranges are inclusive. For example:
+
+ - *wq_cpu_set=0.3-7* will use CPUs 0, 3, 4, 5, 6 and 7.
+
+ - *wq_cpu_set=0.4.1.5* will use CPUs 0, 1, 4 and 5.
+
+ This option is similar to the taskset bitmask except that the comma separator
+ is replaced with a dot. The reason for this is that the mount option parser
+ uses commas to separate mount options.
+
+ If *wq_cpu_set* option is specificed and the *thread_pool* option is not, the
+ number of default max thread pool size will be set to the number of online
+ CPUs in the specified CPU set plus 2, if and only if the resulting number is
+ less than 8.
+
+ If *wq_cpu_set* option is specificed and the *thread_pool* option is also
+ specified, the thread pool size will be set to the value of *thread_pool*
+ option.
+
+
DEPRECATED MOUNT OPTIONS
^^^^^^^^^^^^^^^^^^^^^^^^
--
Ammar Faizi
