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sched_ext: Add SCX_ENQ_IGNORE_CAPS for in-place restore

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A SAVE/RESTORE requeue re-inserts a running task in place and is immediately
followed by set_next_task_scx(). It is not a real scheduling event: the task
is already admitted to its cid and must return to the local DSQ
unconditionally.

scx_caps_for_enq() maps an enqueue to the cap its local-DSQ insert requires.
Add SCX_ENQ_IGNORE_CAPS, set it on the RESTORE-in-place branch of
enqueue_task_scx(), and have scx_caps_for_enq() require no caps for it, so
the cid admission gate never diverts an in-place restore to the reject DSQ.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
This commit is contained in:
Tejun Heo 2026-07-13 22:18:43 -10:00
parent 75a8c8202c
commit 8b17523479
3 changed files with 9 additions and 2 deletions
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7
kernel/sched/ext/ext.c
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@ -1878,10 +1878,13 @@ static void enqueue_task_scx(struct rq *rq, struct task_struct *p, int core_enq_
* Restoring a running task will be immediately followed by
* set_next_task_scx() which expects the task to not be on the BPF
* scheduler as tasks can only start running through local DSQs. Force
* direct-dispatch into the local DSQ by setting the sticky_cpu.
* direct-dispatch into the local DSQ by setting the sticky_cpu. Mark
* IGNORE_CAPS to force entry into the local DSQ.
*/
if (unlikely(enq_flags & ENQUEUE_RESTORE) && task_current(rq, p))
if (unlikely(enq_flags & ENQUEUE_RESTORE) && task_current(rq, p)) {
sticky_cpu = cpu_of(rq);
enq_flags |= SCX_ENQ_IGNORE_CAPS;
}
if (p->scx.flags & SCX_TASK_QUEUED) {
WARN_ON_ONCE(!task_runnable(p));

1
kernel/sched/ext/internal.h
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@ -1568,6 +1568,7 @@ enum scx_enq_flags {
SCX_ENQ_DSQ_PRIQ = 1LLU << 57,
SCX_ENQ_NESTED = 1LLU << 58,
SCX_ENQ_GDSQ_FALLBACK = 1LLU << 59, /* fell back to global DSQ */
SCX_ENQ_IGNORE_CAPS = 1LLU << 60, /* admit to local DSQ ignoring caps */
};
enum scx_deq_flags {

3
kernel/sched/ext/sub.h
View File

@ -112,6 +112,9 @@ static inline u64 scx_missing_caps(struct scx_sched *sch, s32 cpu, u64 needed)
/* map @enq_flags to the SCX_CAP_* bit required for the local-DSQ insert */
static inline u64 scx_caps_for_enq(u64 enq_flags)
{
/* a restored task must be put into the local DSQ regardless of caps */
if (enq_flags & SCX_ENQ_IGNORE_CAPS)
return 0;
return 0;
}