From: Tao Cui <[email protected]> Document the BPF cost model attachment in the io.cost.model section of the cgroup v2 documentation: attaching an iocost_model_ops struct_ops to a device by its major:minor, the model=bpf readback while attached (ctrl keeps describing the coefficients), that detaching restores the builtin model, and that writes never select a model.
Signed-off-by: Tao Cui <[email protected]> --- Documentation/admin-guide/cgroup-v2.rst | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index 8d2603751c51..306cc929c88d 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -2117,8 +2117,30 @@ IO Interface Files ===== ================================ ctrl "auto" or "user" model The cost model in use - "linear" + or "bpf" while a BPF model is + attached ===== ================================ + When CONFIG_BLK_CGROUP_IOCOST_BPF is enabled, a BPF cost model + can be attached to a device by loading an "iocost_model_ops" + struct_ops with the whole disk's major:minor in its "dev" member + (a partition's major:minor is rejected); + attaching switches the device's pricing to the model, detaching + the struct_ops restores the builtin linear model. While a model + is attached, "model" reads back "bpf"; "ctrl" keeps describing + the builtin coefficients, which are inert while the model is + attached: coefficient writes are stored and take effect again + after the struct_ops is detached, and the automatic profile + stepping does not switch profiles. Writing "ctrl=bpf" or + "model=bpf" is accepted as a no-op so a saved configuration + still parses, but re-attaching the model requires loading the + struct_ops again, not writing to this file. Attaching + implicitly enables the controller if needed (disabling wbt + like io.cost.qos does); detaching does not disable it again, + and writing "enable=0" to io.cost.qos suspends the model's + pricing until the controller is re-enabled, while it stays + attached. + When "ctrl" is "auto", the kernel may change all parameters dynamically. When "ctrl" is set to "user" or any other parameters are written to, "ctrl" become "user" and the -- 2.43.0
