Re: [GIT PULL] sched_ext: Initial pull request for v6.11

[Tejun Heo <tj@kernel.org>]

Hello,

On Fri, Aug 02, 2024 at 01:10:18PM +0200, Peter Zijlstra wrote:
> On Tue, Jul 30, 2024 at 03:36:27PM -1000, Tejun Heo wrote:
...
> > Maybe, but at the same time, it's also just some isolated cruft that enables
> > UP support, so both sides of the scale seem similarly light-weight? I lean
> > towards "why not support it?" but don't feel particularly strongly about it.
> 
> So you're basically looking for something like this?
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index a9f655025607..69ec02a28117 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -5772,7 +5772,6 @@ static inline void schedule_debug(struct task_struct *prev, bool preempt)
>  static void put_prev_task_balance(struct rq *rq, struct task_struct *prev,
>  				  struct rq_flags *rf)
>  {
> -#ifdef CONFIG_SMP
>  	const struct sched_class *class;
>  	/*
>  	 * We must do the balancing pass before put_prev_task(), such
> @@ -5783,10 +5782,9 @@ static void put_prev_task_balance(struct rq *rq, struct task_struct *prev,
>  	 * a runnable task of @class priority or higher.
>  	 */
>  	for_class_range(class, prev->sched_class, &idle_sched_class) {
> -		if (class->balance(rq, prev, rf))
> +		if (class->balance && class->balance(rq, prev, rf))
>  			break;
>  	}
> -#endif
>  
>  	put_prev_task(rq, prev);
>  }
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 4c36cc680361..40f3dc436f4f 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -2296,8 +2296,8 @@ struct sched_class {
>  	void (*put_prev_task)(struct rq *rq, struct task_struct *p);
>  	void (*set_next_task)(struct rq *rq, struct task_struct *p, bool first);
>  
> -#ifdef CONFIG_SMP
>  	int (*balance)(struct rq *rq, struct task_struct *prev, struct rq_flags *rf);
> +#ifdef CONFIG_SMP
>  	int  (*select_task_rq)(struct task_struct *p, int task_cpu, int flags);
>  
>  	struct task_struct * (*pick_task)(struct rq *rq);

Yes, exactly. This is how it was implemented in the first RFC patchset. If
you're okay with the above, I'd love to go back to it.

Thanks.

-- 
tejun