Re: [PATCH v33 1/7] sched/psi: Preserve sleep-persistent PSI flags on off-CPU sleeping dequeues

[Peter Zijlstra]

On Fri, Oct 23, 2026 at 10:04:12PM +0000, John Stultz wrote:
> diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
> index ebe0a7765f98e..20820fe1021a1 100644
> --- a/kernel/sched/stats.h
> +++ b/kernel/sched/stats.h
> @@ -175,12 +175,28 @@ static inline void psi_dequeue(struct task_struct *p, int flags)
>  	 * Do nothing here.
>  	 *
>  	 * In the SCHED_PROXY_EXECUTION case we may do sleeping
> -	 * dequeues that are not followed by a task switch, so check
> -	 * TSK_ONCPU is set to ensure the task switch is imminent.
> -	 * Otherwise clear the flags as usual.
> +	 * dequeues that are not followed by a task switch. If TSK_ONCPU
> +	 * is not set (meaning we already switched away while the task
> +	 * stayed on the rq as a blocked donor), handle the sleeping
> +	 * state transition here so sleep-persistent states (TSK_MEMSTALL,
> +	 * TSK_IOWAIT) are preserved.
>  	 */
> -	if ((flags & DEQUEUE_SLEEP) && (p->psi_flags & TSK_ONCPU))
> +	if (flags & DEQUEUE_SLEEP) {
> +		int clear = TSK_RUNNING, set = 0;
> +
> +		if (p->psi_flags & TSK_ONCPU)
> +			return;
> +		if (p->se.sched_delayed)
> +			return;

Must this really be sched_delayed, that is, cannot p->is_blocked be used
here? I'm trying to push sched_delayed into fair.c if at all possible.

> +
> +		if (p->in_memstall)
> +			clear |= TSK_MEMSTALL_RUNNING;
> +		if (p->in_iowait)
> +			set |= TSK_IOWAIT;
> +
> +		psi_task_change(p, clear, set);
>  		return;
> +	}
>  
>  	/*
>  	 * When migrating a task to another CPU, clear all psi
> -- 
> 2.56.0.257.gf7497c7d27-goog
>