Re: [PATCH 04/16] sched_ext: Relocate cpu_acquire/cpu_release to end of struct sched_ext_ops

[Cheng-Yang Chou <yphbchou0911@gmail.com>]

Hi Tejun,

On Mon, Apr 20, 2026 at 09:19:33PM -1000, Tejun Heo wrote:
> cpu_acquire and cpu_release are deprecated and slated for removal. Move
> their declarations to the end of struct sched_ext_ops so an upcoming
> cid-form struct (sched_ext_ops_cid) can omit them entirely without
> disturbing the offsets of the shared fields.
> 
> Switch the two SCX_HAS_OP() callers for these ops to direct field checks
> since the relocated ops sit outside the SCX_OPI_END range covered by the
> has_op bitmap.
> 
> scx_kf_allow_flags[] auto-sizes to the highest used SCX_OP_IDX, so
> SCX_OP_IDX(cpu_release) moving to a higher index just enlarges the
> sparse array; the lookup logic is unchanged.
> 
> Signed-off-by: Tejun Heo <tj@kernel.org>

Looks good.

Reviewed-by: Cheng-Yang Chou <yphbchou0911@gmail.com>

> ---
>  kernel/sched/ext.c          |  4 +--
>  kernel/sched/ext_internal.h | 54 ++++++++++++++++++++++---------------
>  2 files changed, 34 insertions(+), 24 deletions(-)
> 
> diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
> index 9e802d73f205..74e4271e44e9 100644
> --- a/kernel/sched/ext.c
> +++ b/kernel/sched/ext.c
> @@ -2813,7 +2813,7 @@ static int balance_one(struct rq *rq, struct task_struct *prev)
>  		 * core. This callback complements ->cpu_release(), which is
>  		 * emitted in switch_class().
>  		 */
> -		if (SCX_HAS_OP(sch, cpu_acquire))
> +		if (sch->ops.cpu_acquire)
>  			SCX_CALL_OP(sch, cpu_acquire, rq, cpu, NULL);
>  		rq->scx.cpu_released = false;
>  	}
> @@ -2959,7 +2959,7 @@ static void switch_class(struct rq *rq, struct task_struct *next)
>  	 *  next time that balance_one() is invoked.
>  	 */
>  	if (!rq->scx.cpu_released) {
> -		if (SCX_HAS_OP(sch, cpu_release)) {
> +		if (sch->ops.cpu_release) {
>  			struct scx_cpu_release_args args = {
>  				.reason = preempt_reason_from_class(next_class),
>  				.task = next,
> diff --git a/kernel/sched/ext_internal.h b/kernel/sched/ext_internal.h
> index 350b84876b2a..1d73fcc19aaf 100644
> --- a/kernel/sched/ext_internal.h
> +++ b/kernel/sched/ext_internal.h
> @@ -555,28 +555,6 @@ struct sched_ext_ops {
>  	 */
>  	void (*update_idle)(s32 cpu, bool idle);
>  
> -	/**
> -	 * @cpu_acquire: A CPU is becoming available to the BPF scheduler
> -	 * @cpu: The CPU being acquired by the BPF scheduler.
> -	 * @args: Acquire arguments, see the struct definition.
> -	 *
> -	 * A CPU that was previously released from the BPF scheduler is now once
> -	 * again under its control.
> -	 */
> -	void (*cpu_acquire)(s32 cpu, struct scx_cpu_acquire_args *args);
> -
> -	/**
> -	 * @cpu_release: A CPU is taken away from the BPF scheduler
> -	 * @cpu: The CPU being released by the BPF scheduler.
> -	 * @args: Release arguments, see the struct definition.
> -	 *
> -	 * The specified CPU is no longer under the control of the BPF
> -	 * scheduler. This could be because it was preempted by a higher
> -	 * priority sched_class, though there may be other reasons as well. The
> -	 * caller should consult @args->reason to determine the cause.
> -	 */
> -	void (*cpu_release)(s32 cpu, struct scx_cpu_release_args *args);
> -
>  	/**
>  	 * @init_task: Initialize a task to run in a BPF scheduler
>  	 * @p: task to initialize for BPF scheduling
> @@ -867,6 +845,38 @@ struct sched_ext_ops {
>  
>  	/* internal use only, must be NULL */
>  	void __rcu *priv;
> +
> +	/*
> +	 * Deprecated callbacks. Kept at the end of the struct so the cid-form
> +	 * struct (sched_ext_ops_cid) can omit them without affecting the
> +	 * shared field offsets. Use SCX_ENQ_IMMED instead. Sitting past
> +	 * SCX_OPI_END means has_op doesn't cover them, so SCX_HAS_OP() cannot
> +	 * be used; callers must test sch->ops.cpu_acquire / cpu_release
> +	 * directly.
> +	 */
> +
> +	/**
> +	 * @cpu_acquire: A CPU is becoming available to the BPF scheduler
> +	 * @cpu: The CPU being acquired by the BPF scheduler.
> +	 * @args: Acquire arguments, see the struct definition.
> +	 *
> +	 * A CPU that was previously released from the BPF scheduler is now once
> +	 * again under its control. Deprecated; use SCX_ENQ_IMMED instead.
> +	 */
> +	void (*cpu_acquire)(s32 cpu, struct scx_cpu_acquire_args *args);
> +
> +	/**
> +	 * @cpu_release: A CPU is taken away from the BPF scheduler
> +	 * @cpu: The CPU being released by the BPF scheduler.
> +	 * @args: Release arguments, see the struct definition.
> +	 *
> +	 * The specified CPU is no longer under the control of the BPF
> +	 * scheduler. This could be because it was preempted by a higher
> +	 * priority sched_class, though there may be other reasons as well. The
> +	 * caller should consult @args->reason to determine the cause.
> +	 * Deprecated; use SCX_ENQ_IMMED instead.
> +	 */
> +	void (*cpu_release)(s32 cpu, struct scx_cpu_release_args *args);
>  };
>  
>  enum scx_opi {
> -- 
> 2.53.0
> 
> 

-- 
Cheers,
Cheng-Yang