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 ctrl= writes never select a model.
Signed-off-by: Tao Cui <[email protected]> --- Documentation/admin-guide/cgroup-v2.rst | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index 7fe950425216..5e780bdcf324 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -2117,8 +2117,27 @@ IO Interface Files ===== ================================ ctrl "auto" or "user" model The cost model in use - "linear" + or "bpf" while the BPF model + is in use ===== ================================ + 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 creates the + controller if needed, like an io.cost.model write does, and + switches the device's pricing to the model; enabling and + disabling the controller stays with io.cost.qos. While a model + is attached, "model" selects between it and the builtin model: + "model=bpf" switches to the attached model and "model=linear" + switches back to the builtin model, and neither detaches the + struct_ops; only detaching removes the model, after which + "model=bpf" fails. "ctrl" keeps describing the builtin + coefficients, which are kept while the BPF model is in use and + take effect again when switched back, and the automatic profile + stepping does not switch profiles while the BPF model is in + use. + 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
