linux-kernel - Re: [PATCH v7 6/7] sched: replace capacity

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Message-ID: <20141009121643.GQ4750@worktop.programming.kicks-ass.net>
Date:	Thu, 9 Oct 2014 14:16:43 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	mingo@...nel.org, linux-kernel@...r.kernel.org,
	preeti@...ux.vnet.ibm.com, Morten.Rasmussen@....com,
	kamalesh@...ux.vnet.ibm.com, linux@....linux.org.uk,
	linux-arm-kernel@...ts.infradead.org, riel@...hat.com,
	efault@....de, nicolas.pitre@...aro.org,
	linaro-kernel@...ts.linaro.org, daniel.lezcano@...aro.org,
	dietmar.eggemann@....com, pjt@...gle.com, bsegall@...gle.com
Subject: Re: [PATCH v7 6/7] sched: replace capacity_factor by usage

On Tue, Oct 07, 2014 at 02:13:36PM +0200, Vincent Guittot wrote:
> +static inline bool
> +group_has_capacity(struct lb_env *env, struct sg_lb_stats *sgs)
>  {
> +	if ((sgs->group_capacity * 100) >
> +			(sgs->group_usage * env->sd->imbalance_pct))
> +		return true;

Why the imb_pct there? We're looking for 100% utilization, not 130 or
whatnot, right?

> +	if (sgs->sum_nr_running < sgs->group_weight)
> +		return true;

With the code as it stands, this is the cheaper test (no mults) so why
is it second?

> +	return false;
> +}
>  
> +static inline bool
> +group_is_overloaded(struct lb_env *env, struct sg_lb_stats *sgs)
> +{
> +	if (sgs->sum_nr_running <= sgs->group_weight)
> +		return false;
> +
> +	if ((sgs->group_capacity * 100) <
> +			(sgs->group_usage * env->sd->imbalance_pct))
> +		return true;
>  
> +	return false;
>  }

Same thing here wrt imb_pct
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