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sched_ext: Properly mark SCX-internal migrations via sticky_cpu

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Reposition the setting and clearing of sticky_cpu to better define the
scope of SCX-internal migrations.

This ensures @sticky_cpu is set for the entire duration of an internal
migration (from dequeue through enqueue), making it a reliable indicator
that an SCX-internal migration is in progress. The dequeue and enqueue
paths can then use @sticky_cpu to identify internal migrations and skip
BPF scheduler notifications accordingly.

This prepares for a later commit fixing the ops.dequeue() semantics.
No functional change intended.

Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Andrea Righi 2026-02-18 09:32:15 +01:00 committed by Tejun Heo
parent 6de23f81a5
commit b75aaea24c
1 changed files with 8 additions and 5 deletions
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13
kernel/sched/ext.c
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@ -1476,9 +1476,6 @@ static void enqueue_task_scx(struct rq *rq, struct task_struct *p, int enq_flags
enq_flags |= rq->scx.extra_enq_flags;
if (sticky_cpu >= 0)
p->scx.sticky_cpu = -1;
/*
* Restoring a running task will be immediately followed by
* set_next_task_scx() which expects the task to not be on the BPF
@ -1509,6 +1506,9 @@ static void enqueue_task_scx(struct rq *rq, struct task_struct *p, int enq_flags
dl_server_start(&rq->ext_server);
do_enqueue_task(rq, p, enq_flags, sticky_cpu);
if (sticky_cpu >= 0)
p->scx.sticky_cpu = -1;
out:
rq->scx.flags &= ~SCX_RQ_IN_WAKEUP;
@ -1670,10 +1670,13 @@ static void move_remote_task_to_local_dsq(struct task_struct *p, u64 enq_flags,
{
lockdep_assert_rq_held(src_rq);
/* the following marks @p MIGRATING which excludes dequeue */
/*
* Set sticky_cpu before deactivate_task() to properly mark the
* beginning of an SCX-internal migration.
*/
p->scx.sticky_cpu = cpu_of(dst_rq);
deactivate_task(src_rq, p, 0);
set_task_cpu(p, cpu_of(dst_rq));
p->scx.sticky_cpu = cpu_of(dst_rq);
raw_spin_rq_unlock(src_rq);
raw_spin_rq_lock(dst_rq);