Commit b75aaea2 authored by Andrea Righi's avatar Andrea Righi Committed by Tejun Heo
Browse files

sched_ext: Properly mark SCX-internal migrations via sticky_cpu 



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: default avatarAndrea Righi <arighi@nvidia.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 6de23f81

kernel/sched/ext.c

+8 −5
Original line number Diff line number Diff line
@@ -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);