linux-kernel - Re: [RFC PATCH v3 07/10] sched/fair: Introduce an energy estimation helper function

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Message-ID: <20180619095140.GE9208@codeaurora.org>
Date:   Tue, 19 Jun 2018 15:21:40 +0530
From:   Pavan Kondeti <pkondeti@...eaurora.org>
To:     Quentin Perret <quentin.perret@....com>
Cc:     peterz@...radead.org, rjw@...ysocki.net,
        gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, mingo@...hat.com,
        dietmar.eggemann@....com, morten.rasmussen@....com,
        chris.redpath@....com, patrick.bellasi@....com,
        valentin.schneider@....com, vincent.guittot@...aro.org,
        thara.gopinath@...aro.org, viresh.kumar@...aro.org,
        tkjos@...gle.com, joelaf@...gle.com, smuckle@...gle.com,
        adharmap@...cinc.com, skannan@...cinc.com, juri.lelli@...hat.com,
        edubezval@...il.com, srinivas.pandruvada@...ux.intel.com,
        currojerez@...eup.net, javi.merino@...nel.org
Subject: Re: [RFC PATCH v3 07/10] sched/fair: Introduce an energy estimation
 helper function

On Mon, May 21, 2018 at 03:25:02PM +0100, Quentin Perret wrote:

<snip>

>  
> +/*
> + * Returns the util of "cpu" if "p" wakes up on "dst_cpu".
> + */
> +static unsigned long cpu_util_next(int cpu, struct task_struct *p, int dst_cpu)
> +{
> +	unsigned long util, util_est;
> +	struct cfs_rq *cfs_rq;
> +
> +	/* Task is where it should be, or has no impact on cpu */
> +	if ((task_cpu(p) == dst_cpu) || (cpu != task_cpu(p) && cpu != dst_cpu))
> +		return cpu_util(cpu);
> +
> +	cfs_rq = &cpu_rq(cpu)->cfs;
> +	util = READ_ONCE(cfs_rq->avg.util_avg);
> +
> +	if (dst_cpu == cpu)
> +		util += task_util(p);
> +	else
> +		util = max_t(long, util - task_util(p), 0);
> +
> +	if (sched_feat(UTIL_EST)) {
> +		util_est = READ_ONCE(cfs_rq->avg.util_est.enqueued);
> +		if (dst_cpu == cpu)
> +			util_est += _task_util_est(p);
> +		else
> +			util_est = max_t(long, util_est - _task_util_est(p), 0);

For UTIL_EST case, the waking task will not have any contribution in the
previous CPU's util_est. So we can just use the previous CPU util_est as is.

> +		util = max(util, util_est);
> +	}
> +
> +	return min_t(unsigned long, util, capacity_orig_of(cpu));
> +}
> +

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