diff options
| author | Cheng-Yang Chou <yphbchou0911@gmail.com> | 2026-03-27 17:50:39 +0800 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2026-03-27 07:33:08 -1000 |
| commit | 238aa43f0b77ea7db7f306e010f688c77439ee62 (patch) | |
| tree | 11862610c986c04a0950f53e72e15e841b32e0ac /kernel | |
| parent | d6edb15ad92cb61386c46662a5ae245c7feac5f0 (diff) | |
sched_ext: Document why built-in DSQs are unsupported sources in scx_bpf_dsq_move_to_local()
Add a comment explaining the design intent behind rejecting built-in DSQs
(%SCX_DSQ_GLOBAL and %SCX_DSQ_LOCAL*) as sources. Local DSQs support
reenqueueing but the BPF scheduler cannot directly iterate or move tasks
from them. %SCX_DSQ_GLOBAL is similar but also doesn't support
reenqueueing because it maps to multiple per-node DSQs, making the scope
difficult to define.
Also annotate @dsq_id to make clear it must be a user-created DSQ.
Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/sched/ext.c | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index 7043fb941130..bfe923b7ffe0 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -8212,7 +8212,7 @@ __bpf_kfunc void scx_bpf_dispatch_cancel(const struct bpf_prog_aux *aux) /** * scx_bpf_dsq_move_to_local - move a task from a DSQ to the current CPU's local DSQ - * @dsq_id: DSQ to move task from + * @dsq_id: DSQ to move task from. Must be a user-created DSQ * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * @enq_flags: %SCX_ENQ_* * @@ -8220,6 +8220,14 @@ __bpf_kfunc void scx_bpf_dispatch_cancel(const struct bpf_prog_aux *aux) * local DSQ for execution with @enq_flags applied. Can only be called from * ops.dispatch(). * + * Built-in DSQs (%SCX_DSQ_GLOBAL and %SCX_DSQ_LOCAL*) are not supported as + * sources. Local DSQs support reenqueueing (a task can be picked up for + * execution, dequeued for property changes, or reenqueued), but the BPF + * scheduler cannot directly iterate or move tasks from them. %SCX_DSQ_GLOBAL + * is similar but also doesn't support reenqueueing, as it maps to multiple + * per-node DSQs making the scope difficult to define; this may change in the + * future. + * * This function flushes the in-flight dispatches from scx_bpf_dsq_insert() * before trying to move from the specified DSQ. It may also grab rq locks and * thus can't be called under any BPF locks. |