From: Tao Cui <[email protected]> Document the "bpf" value of the ctrl key of io.cost.model and the iocost_model_ops struct_ops it selects, in the io.cost.model section of the cgroup v2 documentation: the registration precondition and single-instance limit, the scalar arguments, the vtime clamp and the delegation-to-builtin semantics of a zero return value.
Signed-off-by: Tao Cui <[email protected]> --- Documentation/admin-guide/cgroup-v2.rst | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index 8d2603751c51a..54b0574ce586c 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -2115,10 +2115,24 @@ IO Interface Files are defined. ===== ================================ - ctrl "auto" or "user" + ctrl "auto", "user" or "bpf" model The cost model in use - "linear" ===== ================================ + When "ctrl" is "bpf" (only available when + CONFIG_BLK_CGROUP_IOCOST_BPF is enabled), cost calculation for + the device is dispatched to the BPF program registered against + the iocost_model_ops struct_ops. Writing "bpf" fails with -EINVAL + until such a program is registered, and at most one program can + be registered system-wide. The model is called with scalar + arguments (operation, size, sector, cgroup cursor, css id of the + issuing cgroup, flags; see include/linux/blk-iocost.h for their + meaning) and returns a cost in vtime units, clamped by the kernel + to 1 second of device time per IO. A return value of 0 delegates + the IO back to the builtin linear formula, so a model which only + handles some IO types cannot make the rest free. Devices which + don't opt in keep the builtin linear model unchanged. + 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
