From: Tao Cui <redacted>
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 <redacted>
---
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