Re: [PATCH 02/13] sched_ext: Make slice values tunable and use shorter slice in bypass mode

[Dan Schatzberg <schatzberg.dan@gmail.com>]

On Sun, Nov 09, 2025 at 08:31:01AM -1000, Tejun Heo wrote:
> @@ -919,7 +948,7 @@ static void dsq_mod_nr(struct scx_dispatch_q *dsq, s32 delta)
>  
>  static void refill_task_slice_dfl(struct scx_sched *sch, struct task_struct *p)
>  {
> -	p->scx.slice = SCX_SLICE_DFL;
> +	p->scx.slice = scx_slice_dfl;

Do you need to use READ_ONCE here given that this can be modified concurrently?

>  	__scx_add_event(sch, SCX_EV_REFILL_SLICE_DFL, 1);
>  }
>  
> @@ -2892,7 +2921,7 @@ void init_scx_entity(struct sched_ext_entity *scx)
>  	INIT_LIST_HEAD(&scx->runnable_node);
>  	scx->runnable_at = jiffies;
>  	scx->ddsp_dsq_id = SCX_DSQ_INVALID;
> -	scx->slice = SCX_SLICE_DFL;
> +	scx->slice = scx_slice_dfl;
>  }
>  
>  void scx_pre_fork(struct task_struct *p)
> @@ -3770,6 +3799,7 @@ static void scx_bypass(bool bypass)
>  		WARN_ON_ONCE(scx_bypass_depth <= 0);
>  		if (scx_bypass_depth != 1)
>  			goto unlock;
> +		scx_slice_dfl = scx_slice_bypass_us * NSEC_PER_USEC;

Similarly WRITE_ONCE here

>  		bypass_timestamp = ktime_get_ns();
>  		if (sch)
>  			scx_add_event(sch, SCX_EV_BYPASS_ACTIVATE, 1);
> @@ -3778,6 +3808,7 @@ static void scx_bypass(bool bypass)
>  		WARN_ON_ONCE(scx_bypass_depth < 0);
>  		if (scx_bypass_depth != 0)
>  			goto unlock;
> +		scx_slice_dfl = scx_slice_dfl_us * NSEC_PER_USEC;

And here

>  		if (sch)
>  			scx_add_event(sch, SCX_EV_BYPASS_DURATION,
>  				      ktime_get_ns() - bypass_timestamp);
> @@ -4776,7 +4807,7 @@ static int scx_enable(struct sched_ext_ops *ops, struct bpf_link *link)
>  			queue_flags |= DEQUEUE_CLASS;
>  
>  		scoped_guard (sched_change, p, queue_flags) {
> -			p->scx.slice = SCX_SLICE_DFL;
> +			p->scx.slice = scx_slice_dfl;

And here
>  			p->sched_class = new_class;
>  		}
>  	}
> -- 
> 2.51.1
>