Re: [PATCH v4 14/15] Remove the ext server BW before changing tasks to FAIR

[Andrea Righi]

Hi Joel,

On Tue, Jun 17, 2025 at 04:05:17PM -0400, Joel Fernandes wrote:
> Signed-off-by: Joel Fernandes <joelagnelf@xxxxxxxxxx>
> ---
>  kernel/sched/ext.c | 39 +++++++++++++++++++++++++--------------
>  1 file changed, 25 insertions(+), 14 deletions(-)
> 
> diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
> index 84ccab8cb838..23e5711bc4fc 100644
> --- a/kernel/sched/ext.c
> +++ b/kernel/sched/ext.c
> @@ -4960,6 +4960,31 @@ static void scx_disable_workfn(struct kthread_work *work)
>  
>  	scx_init_task_enabled = false;
>  
> +	for_each_possible_cpu(cpu) {
> +		struct rq *rq = cpu_rq(cpu);
> +		struct rq_flags rf;
> +
> +		/*
> +		 * Invalidate all the rq clocks to prevent getting outdated
> +		 * rq clocks from a previous scx scheduler.
> +		 */
> +		scx_rq_clock_invalidate(rq);

We're also calling scx_rq_clock_invalidate(rq) twice (see below).

> +
> +		/*
> +		 * We are unloading the sched_ext scheduler, we do not need its
> +		 * DL server bandwidth anymore, remove it for all CPUs. Whenever
> +		 * the first SCX task is enqueued (when scx is re-loaded), its DL
> +		 * server bandwidth will be re-initialized.
> +		 */
> +		rq_lock_irqsave(rq, &rf);
> +		update_rq_clock(rq);
> +		if (dl_server_active(&rq->ext_server))
> +			dl_server_stop(&rq->ext_server);
> +		dl_server_remove_params(&rq->ext_server);
> +		rq_unlock_irqrestore(rq, &rf);
> +	}
> +
> +
>  	scx_task_iter_start(&sti);
>  	while ((p = scx_task_iter_next_locked(&sti))) {
>  		const struct sched_class *old_class = p->sched_class;
> @@ -4985,26 +5010,12 @@ static void scx_disable_workfn(struct kthread_work *work)
>  
>  	for_each_possible_cpu(cpu) {
>  		struct rq *rq = cpu_rq(cpu);
> -		struct rq_flags rf;
>  
>  		/*
>  		 * Invalidate all the rq clocks to prevent getting outdated
>  		 * rq clocks from a previous scx scheduler.
>  		 */
>  		scx_rq_clock_invalidate(rq);
> -
> -		/*
> -		 * We are unloading the sched_ext scheduler, we do not need its
> -		 * DL server bandwidth anymore, remove it for all CPUs. Whenever
> -		 * the first SCX task is enqueued (when scx is re-loaded), its DL
> -		 * server bandwidth will be re-initialized.
> -		 */
> -		rq_lock_irqsave(rq, &rf);
> -		update_rq_clock(rq);
> -		if (dl_server_active(&rq->ext_server))
> -			dl_server_stop(&rq->ext_server);
> -		dl_server_remove_params(&rq->ext_server);
> -		rq_unlock_irqrestore(rq, &rf);
>  	}

We should probably remove this for_each_possible_cpu() completely.

>  
>  	/* no task is on scx, turn off all the switches and flush in-progress calls */
> -- 
> 2.43.0
> 

Thanks,
-Andrea