> blk-iocost: add BPF struct_ops cost model support
TL;DR: Documentation issue only: cgroup-v2.rst isn't updated for io.cost.model
accepting "model=bpf", and writing "model=linear" now switches a device off an
attached BPF model, which may surprise existing tools.
> diff --git a/block/blk-iocost.c b/block/blk-iocost.c
> index 2745bffcd5ee..509ae36f99ed 100644
> --- a/block/blk-iocost.c
> +++ b/block/blk-iocost.c
[ ... ]
> @@ -3536,9 +3961,25 @@ static ssize_t ioc_cost_model_write(struct
> kernfs_open_file *of, char *input,
> continue;
> case COST_MODEL:
> match_strlcpy(buf, &args[0], sizeof(buf));
> - if (strcmp(buf, "linear"))
> - goto unlock;
> - continue;
> + if (!strcmp(buf, "linear")) {
> + /* staged and committed below, so a parse
> + * error later in the same write leaves
> + * the model selection untouched
> + */
> + new_model = NULL;
> + model_write = true;
> + continue;
> + }
> + if (!strcmp(buf, "bpf")) {
> + new_model = rcu_dereference_protected(
> + ioc->attached,
> + lockdep_is_held(&ioc->lock));
> + if (!new_model)
> + goto unlock;
> + model_write = true;
> + continue;
> + }
> + goto unlock;
> }
Does this change to the io.cost.model interface need a matching update to
Documentation/admin-guide/cgroup-v2.rst?
ioc_cost_model_write() now accepts "model=bpf", and "model=linear" is no
longer only a value check. It now clears ioc->model and moves the device
off an attached BPF model. ioc_cost_model_prfill() can also print
"model=bpf".
The documentation still describes the key as:
model The cost model in use - "linear"
and says nothing about "bpf" or the new effect of writing "linear".
Existing tools that write lines like "MAJ:MIN ctrl=user model=linear
rbps=..." will now silently switch a device away from an attached BPF
model. Could cgroup-v2.rst be updated to cover the new value and the
changed semantics?
---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
CI run summary: https://github.com/kernel-patches/bpf/actions/runs/37124306614
