Re: [PATCH v3 02/10] sched/fair: Credit a persistent, queue-depth-scaled vlag margin

[K Prateek Nayak]

Hello Wanpeng,

On 6/12/2026 7:03 AM, Wanpeng Li wrote:
> -	/* Already eligible: nothing to do. */
> -	if (vlag >= 0)
> -		return;
> +	/* Clamp the margin to entity_lag()'s bound so place_entity() keeps it. */
> +	max_slice = cfs_rq_max_slice(cfs_rq) + TICK_NSEC;
> +	lag_limit = calc_delta_fair(max_slice, se);
> +	margin = eevdf_persistent_margin(cfs_rq, se);
> +	if (lag_limit && margin > lag_limit)
> +		margin = lag_limit;
> +	if (vlag >= 0) {
> +		if ((u64)vlag >= margin)
> +			return;
> +		want = margin - (u64)vlag;

And we are making an eligible task more eligible but *where* is this
credit coming from? Someone should be paying the price right?

Just adding an arbitrary credit and then moving the task doing the
yield_to() 0-lag point is simply not fair IMO.

> +	} else {
> +		want = margin + (u64)(-vlag);
> +	}

-- 
Thanks and Regards,
Prateek