Re: [PATCH v3] sched_ext: Implement SCX_OPS_TRACK_MIGRATION

[Andrea Righi <arighi@nvidia.com>]

On Mon, Jun 23, 2025 at 02:30:33PM +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.

Looks good, thanks for moving SCX_ENQ_MIGRATING to the proper place. :)
You already added my reviewed-by line, but just in case:

Reviewed-by: Andrea Righi <arighi@nvidia.com>

-Andrea

> 
> Signed-off-by: Henry Huang <henry.hj@antgroup.com>
> Reviewed-by: Andrea Righi <arighi@nvidia.com>
> ---
>  kernel/sched/ext.c | 26 ++++++++++++++++++++++++--
>  1 file changed, 24 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
> index b498d86..376e028 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 */
> @@ -870,6 +877,7 @@ enum scx_enq_flags {
>  	SCX_ENQ_WAKEUP		= ENQUEUE_WAKEUP,
>  	SCX_ENQ_HEAD		= ENQUEUE_HEAD,
>  	SCX_ENQ_CPU_SELECTED	= ENQUEUE_RQ_SELECTED,
> +	SCX_ENQ_MIGRATING	= ENQUEUE_MIGRATING,
>  
>  	/* high 32bits are SCX specific */
>  
> @@ -913,6 +921,7 @@ enum scx_enq_flags {
>  enum scx_deq_flags {
>  	/* expose select DEQUEUE_* flags as enums */
>  	SCX_DEQ_SLEEP		= DEQUEUE_SLEEP,
> +	SCX_DEQ_MIGRATING	= DEQUEUE_MIGRATING,
>  
>  	/* high 32bits are SCX specific */
>  
> @@ -2390,7 +2399,11 @@ 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 |= SCX_ENQ_MIGRATING;
> +
> +	if (SCX_HAS_OP(sch, runnable) &&
> +	    ((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)
> @@ -2463,6 +2476,9 @@ 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 |= SCX_DEQ_MIGRATING;
> +
>  	ops_dequeue(rq, p, deq_flags);
>  
>  	/*
> @@ -2482,7 +2498,8 @@ 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 & SCX_DEQ_MIGRATING)))
>  		SCX_CALL_OP_TASK(sch, SCX_KF_REST, quiescent, rq, p, deq_flags);
>  
>  	if (deq_flags & SCX_DEQ_SLEEP)
> @@ -5495,6 +5512,11 @@ 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
>