linux-kernel - Re: [PATCH 4/7] sched/fair: Avoid unnecessary balancing of asymmetric capacity groups

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Date:   Mon, 19 Feb 2018 16:10:11 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Morten Rasmussen <morten.rasmussen@....com>
Cc:     mingo@...hat.com, valentin.schneider@....com,
        dietmar.eggemann@....com, vincent.guittot@...aro.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/7] sched/fair: Avoid unnecessary balancing of
 asymmetric capacity groups

On Thu, Feb 15, 2018 at 04:20:51PM +0000, Morten Rasmussen wrote:
> +/*
> + * group_similar_cpu_capacity: Returns true if the minimum capacity of the
> + * compared groups differ by less than 12.5%.
> + */
> +static inline bool
> +group_similar_cpu_capacity(struct sched_group *sg, struct sched_group *ref)
> +{
> +	long diff = sg->sgc->min_capacity - ref->sgc->min_capacity;
> +	long max = max(sg->sgc->min_capacity, ref->sgc->min_capacity);
> +
> +	return abs(diff) < max >> 3;
> +}

This seems a fairly random and dodgy heuristic.