Re: [PATCH v2] sched_ext: include SCX_OPS_TRACK_MIGRATION

[Andrea Righi]

Hi Henry,

On Mon, Jun 23, 2025 at 12:32:20PM +0800, Henry Huang wrote:
> For some BPF-schedulers, they should do something when
> task is doing migration, such as updating per-cpu map.
> If SCX_OPS_TRACK_MIGRATION is set, runnable/quiescent
> would be called whether task is doing migration or not.
> 
> Signed-off-by: Henry Huang <henry.hj@xxxxxxxxxxxx>

Looks good. One last thing, since we're exposing ENQUEUE_MIGRATING and
DEQUEUE_MIGRATING to BPF, can you introduce some scx enums, similar to what
we're doing with DEQUEUE_SLEEP? Something like the following.

With that you can add my:

Reviewed-by: Andrea Righi <arighi@xxxxxxxxxx>

Thanks,
-Andrea

 kernel/sched/ext.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 2f0ab232a2786..bf04cde71b34a 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -918,8 +918,11 @@ enum scx_enq_flags {
 };
 
 enum scx_deq_flags {
+	/* expose select ENQUEUE_* flags as enums */
+	SCX_ENQ_MIGRATING	= ENQUEUE_MIGRATING,
 	/* expose select DEQUEUE_* flags as enums */
 	SCX_DEQ_SLEEP		= DEQUEUE_SLEEP,
+	SCX_DEQ_MIGRATING	= DEQUEUE_MIGRATING,
 
 	/* high 32bits are SCX specific */
 
@@ -2385,10 +2388,10 @@ static void enqueue_task_scx(struct rq *rq, struct task_struct *p, int enq_flags
 	add_nr_running(rq, 1);
 
 	if (task_on_rq_migrating(p))
-		enq_flags |= ENQUEUE_MIGRATING;
+		enq_flags |= SCX_ENQ_MIGRATING;
 
 	if (SCX_HAS_OP(sch, runnable) &&
-	    ((sch->ops.flags & SCX_OPS_TRACK_MIGRATION) || !(enq_flags & ENQUEUE_MIGRATING)))
+	    ((sch->ops.flags & SCX_OPS_TRACK_MIGRATION) || !(enq_flags & SCX_ENQ_MIGRATING)))
 		SCX_CALL_OP_TASK(sch, SCX_KF_REST, runnable, rq, p, enq_flags);
 
 	if (enq_flags & SCX_ENQ_WAKEUP)
@@ -2471,7 +2474,7 @@ static bool dequeue_task_scx(struct rq *rq, struct task_struct *p, int deq_flags
 	}
 
 	if (task_on_rq_migrating(p))
-		deq_flags |= DEQUEUE_MIGRATING;
+		deq_flags |= SCX_DEQ_MIGRATING;
 
 	ops_dequeue(rq, p, deq_flags);
 
@@ -2493,7 +2496,7 @@ static bool dequeue_task_scx(struct rq *rq, struct task_struct *p, int deq_flags
 	}
 
 	if (SCX_HAS_OP(sch, quiescent) &&
-	    ((sch->ops.flags & SCX_OPS_TRACK_MIGRATION) || !(deq_flags & DEQUEUE_MIGRATING)))
+	    ((sch->ops.flags & SCX_OPS_TRACK_MIGRATION) || !(deq_flags & SCX_DEQ_MIGRATING)))
 		SCX_CALL_OP_TASK(sch, SCX_KF_REST, quiescent, rq, p, deq_flags);
 
 	if (deq_flags & SCX_DEQ_SLEEP)

> ---
>  kernel/sched/ext.c | 24 ++++++++++++++++++++++--
>  1 file changed, 22 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
> index b498d86..42c5251 100644
> --- a/kernel/sched/ext.c
> +++ b/kernel/sched/ext.c
> @@ -161,6 +161,12 @@ enum scx_ops_flags {
>  	SCX_OPS_BUILTIN_IDLE_PER_NODE	= 1LLU << 6,
>  
>  	/*
> +	 * If set, runnable/quiescent ops would be called whether the task is
> +	 * doing migration or not.
> +	 */
> +	SCX_OPS_TRACK_MIGRATION		= 1LLU << 7,
> +
> +	/*
>  	 * CPU cgroup support flags
>  	 */
>  	SCX_OPS_HAS_CGROUP_WEIGHT	= 1LLU << 16,	/* DEPRECATED, will be removed on 6.18 */
> @@ -172,6 +178,7 @@ enum scx_ops_flags {
>  					  SCX_OPS_ALLOW_QUEUED_WAKEUP |
>  					  SCX_OPS_SWITCH_PARTIAL |
>  					  SCX_OPS_BUILTIN_IDLE_PER_NODE |
> +					  SCX_OPS_TRACK_MIGRATION |
>  					  SCX_OPS_HAS_CGROUP_WEIGHT,
>  
>  	/* high 8 bits are internal, don't include in SCX_OPS_ALL_FLAGS */
> @@ -2390,7 +2397,11 @@ static void enqueue_task_scx(struct rq *rq, struct task_struct *p, int enq_flags
>  	rq->scx.nr_running++;
>  	add_nr_running(rq, 1);
>  
> -	if (SCX_HAS_OP(sch, runnable) && !task_on_rq_migrating(p))
> +	if (task_on_rq_migrating(p))
> +		enq_flags |= ENQUEUE_MIGRATING;
> +
> +	if (SCX_HAS_OP(sch, runnable) &&
> +	    ((sch->ops.flags & SCX_OPS_TRACK_MIGRATION) || !(enq_flags & ENQUEUE_MIGRATING)))
>  		SCX_CALL_OP_TASK(sch, SCX_KF_REST, runnable, rq, p, enq_flags);
>  
>  	if (enq_flags & SCX_ENQ_WAKEUP)
> @@ -2463,6 +2474,9 @@ static bool dequeue_task_scx(struct rq *rq, struct task_struct *p, int deq_flags
>  		return true;
>  	}
>  
> +	if (task_on_rq_migrating(p))
> +		deq_flags |= DEQUEUE_MIGRATING;
> +
>  	ops_dequeue(rq, p, deq_flags);
>  
>  	/*
> @@ -2482,7 +2496,8 @@ static bool dequeue_task_scx(struct rq *rq, struct task_struct *p, int deq_flags
>  		SCX_CALL_OP_TASK(sch, SCX_KF_REST, stopping, rq, p, false);
>  	}
>  
> -	if (SCX_HAS_OP(sch, quiescent) && !task_on_rq_migrating(p))
> +	if (SCX_HAS_OP(sch, quiescent) &&
> +	    ((sch->ops.flags & SCX_OPS_TRACK_MIGRATION) || !(deq_flags & DEQUEUE_MIGRATING)))
>  		SCX_CALL_OP_TASK(sch, SCX_KF_REST, quiescent, rq, p, deq_flags);
>  
>  	if (deq_flags & SCX_DEQ_SLEEP)
> @@ -5495,6 +5510,11 @@ static int validate_ops(struct scx_sched *sch, const struct sched_ext_ops *ops)
>  		return -EINVAL;
>  	}
>  
> +	if ((ops->flags & SCX_OPS_TRACK_MIGRATION) && (!ops->runnable || !ops->quiescent)) {
> +		scx_error(sch, "SCX_OPS_TRACK_MIGRATION requires ops.runnable() and ops.quiescent() to be implemented");
> +		return -EINVAL;
> +	}
> +
>  	if (ops->flags & SCX_OPS_HAS_CGROUP_WEIGHT)
>  		pr_warn("SCX_OPS_HAS_CGROUP_WEIGHT is deprecated and a noop\n");
>  
> -- 
> Henry
>