Re: [PATCH 4/4] sched/fair: Proportional newidle balance

[Qing Wang]

On Sat, 08 Nov 2025 at 00:06, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>  		if (sd->flags & SD_BALANCE_NEWIDLE) {
> +			unsigned int weight = 1;
> +
> +			if (sched_feat(NI_RANDOM)) {
> +				/*
> +				 * Throw a 1k sided dice; and only run
> +				 * newidle_balance according to the success
> +				 * rate.
> +				 */
> +				u32 d1k = sched_rng() % 1024;
> +				weight = 1 + sd->newidle_ratio;
> +				if (d1k > weight) {
> +					update_newidle_stats(sd, 0);
> +					continue;
> +				}
> +				weight = (1024 + weight/2) / weight;
> +			}

Hi Peter,
I think this optimization approach is excellent. However, there is a small
idea for discussion: would using a count-based window (e.g., if the current
success rate is 50%, then within every window of 100 attempts, exactly 50
are allowed to do balancing) be more stable than using a random number to
trigger balancing?

This is just an idea for discussion. I haven’t implemented and validated
it yet

--
Best regards,
Qing