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From: Peter Zijlstra <peterz@infradead.org>
To: Quentin Perret <quentin.perret@arm.com>
Cc: rjw@rjwysocki.net, linux-kernel@vger.kernel.org,
	linux-pm@vger.kernel.org, gregkh@linuxfoundation.org,
	mingo@redhat.com, dietmar.eggemann@arm.com,
	morten.rasmussen@arm.com, chris.redpath@arm.com,
	patrick.bellasi@arm.com, valentin.schneider@arm.com,
	vincent.guittot@linaro.org, thara.gopinath@linaro.org,
	viresh.kumar@linaro.org, tkjos@google.com,
	joel@joelfernandes.org, smuckle@google.com, adharmap@quicinc.com,
	skannan@quicinc.com, pkondeti@codeaurora.org,
	juri.lelli@redhat.com, edubezval@gmail.com,
	srinivas.pandruvada@linux.intel.com, currojerez@riseup.net,
	javi.merino@kernel.org
Subject: Re: [RFC PATCH v4 09/12] sched/fair: Introduce an energy estimation helper function
Date: Mon, 9 Jul 2018 14:01:38 +0200
Message-ID: <20180709120138.GQ2494@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20180706170443.GE17577@e108498-lin.cambridge.arm.com>

On Fri, Jul 06, 2018 at 06:04:44PM +0100, Quentin Perret wrote:
> 'max_util' is basically the util we use to request an OPP. 'sum_util' is
> how long the CPUs will be running.

A indeed. But yes bit of a mess, but it wants doing I think.
Perhaps a little something like the below... The alternative is two
separate but closely related functions, not sure which is better.


enum schedutil_type {
	frequency_util,
	energy_util,
};

unsigned long
schedutil_freq_util(int cpu, unsigned long util_cfs, enum schedutil_type type)
{
	struct rq *rq = cpu_rq(cpu);
	unsigned long util, irq, max;

	max = arch_scale_cpu_capacity(NULL, cpu);

	if (type == frequency_util && rt_rq_is_runnable(&rq->rt))
		return max;

	/*
	 * Early check to see if IRQ/steal time saturates the CPU, can be
	 * because of inaccuracies in how we track these -- see
	 * update_irq_load_avg().
	 */
	irq = cpu_util_irq(rq);
	if (unlikely(irq >= max))
		return max;

	/*
	 * Because the time spend on RT/DL tasks is visible as 'lost' time to
	 * CFS tasks and we use the same metric to track the effective
	 * utilization (PELT windows are synchronized) we can directly add them
	 * to obtain the CPU's actual utilization.
	 */
	util = util_cfs;
	util += cpu_util_rt(rq);

	if (type == frequency_util) {
		/*
		 * For frequency selection we do not make cpu_util_dl()
		 * a permanent part of this sum because we want to use
		 * cpu_bw_dl() later on, but we need to check if the
		 * CFS+RT+DL sum is saturated (ie. no idle time) such
		 * that we select f_max when there is no idle time.
		 *
		 * NOTE: numerical errors or stop class might cause us
		 * to not quite hit saturation when we should --
		 * something for later.
		 */
		if ((util + cpu_util_dl(rq)) >= max)
			return max;
	} else {
		/*
		 * OTOH, for energy computation we need the estimated
		 * running time, so include util_dl and ignore dl_bw.
		 */
		util += cpu_util_dl(rq);
		if (util >= max)
			return max;
	}

	/*
	 * There is still idle time; further improve the number by using the
	 * irq metric. Because IRQ/steal time is hidden from the task clock we
	 * need to scale the task numbers:
	 *
	 *              1 - irq
	 *   U' = irq + ------- * U
	 *                max
	 */
	util *= (max - irq);
	util /= max;
	util += irq;

	if (type == frequency_util) {
		/*
		 * Bandwidth required by DEADLINE must always be granted
		 * while, for FAIR and RT, we use blocked utilization of
		 * IDLE CPUs as a mechanism to gracefully reduce the
		 * frequency when no tasks show up for longer periods of
		 * time.
		 *
		 * Ideally we would like to set bw_dl as min/guaranteed
		 * freq and util + bw_dl as requested freq. However,
		 * cpufreq is not yet ready for such an interface. So,
		 * we only do the latter for now.
		 */
		util += cpu_bw_dl(rq);
	}

	return min(max, util);
}

  reply index

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-28 11:40 [RFC PATCH v4 00/12] Energy Aware Scheduling Quentin Perret
2018-06-28 11:40 ` [RFC PATCH v4 01/12] sched: Relocate arch_scale_cpu_capacity Quentin Perret
2018-06-28 11:40 ` [RFC PATCH v4 02/12] sched/cpufreq: Factor out utilization to frequency mapping Quentin Perret
2018-06-28 11:40 ` [RFC PATCH v4 03/12] PM: Introduce an Energy Model management framework Quentin Perret
2018-07-05 14:31   ` Peter Zijlstra
2018-07-05 15:24     ` Quentin Perret
2018-07-05 14:39   ` Peter Zijlstra
2018-07-05 15:09     ` Quentin Perret
2018-07-05 15:06   ` Peter Zijlstra
2018-07-05 15:32     ` Quentin Perret
2018-07-06  9:57   ` Vincent Guittot
2018-07-06 10:03     ` Peter Zijlstra
2018-07-06 10:06       ` Quentin Perret
2018-07-06 10:05     ` Quentin Perret
2018-07-09 18:07   ` Dietmar Eggemann
2018-07-10  8:32     ` Quentin Perret
2018-07-16 10:29       ` Quentin Perret
2018-07-17  8:57         ` Dietmar Eggemann
2018-07-17 14:19           ` Quentin Perret
2018-07-17 16:00             ` Dietmar Eggemann
2018-06-28 11:40 ` [RFC PATCH v4 04/12] PM / EM: Expose the Energy Model in sysfs Quentin Perret
2018-06-28 11:40 ` [RFC PATCH v4 05/12] sched/topology: Reference the Energy Model of CPUs when available Quentin Perret
2018-07-05 17:29   ` Peter Zijlstra
2018-07-05 17:48     ` Quentin Perret
2018-07-05 17:33   ` Peter Zijlstra
2018-07-05 17:50     ` Quentin Perret
2018-07-05 18:14       ` Peter Zijlstra
2018-06-28 11:40 ` [RFC PATCH v4 06/12] sched/topology: Lowest energy aware balancing sched_domain level pointer Quentin Perret
2018-06-28 11:40 ` [RFC PATCH v4 07/12] sched/topology: Introduce sched_energy_present static key Quentin Perret
2018-06-28 11:40 ` [RFC PATCH v4 08/12] sched: Add over-utilization/tipping point indicator Quentin Perret
2018-07-06 11:32   ` Peter Zijlstra
2018-07-06 13:20     ` Quentin Perret
2018-07-06 13:24       ` Peter Zijlstra
2018-07-06 13:40         ` Quentin Perret
2018-07-06 11:39   ` Peter Zijlstra
2018-07-06 11:41   ` Peter Zijlstra
2018-07-06 11:49     ` Valentin Schneider
2018-06-28 11:40 ` [RFC PATCH v4 09/12] sched/fair: Introduce an energy estimation helper function Quentin Perret
2018-07-06 13:12   ` Peter Zijlstra
2018-07-06 15:12     ` Quentin Perret
2018-07-06 15:49       ` Peter Zijlstra
2018-07-06 17:04         ` Quentin Perret
2018-07-09 12:01           ` Peter Zijlstra [this message]
2018-07-09 15:28             ` Quentin Perret
2018-07-09 15:42               ` Peter Zijlstra
2018-07-09 16:07                 ` Quentin Perret
2018-07-06 15:50       ` Peter Zijlstra
2018-06-28 11:40 ` [RFC PATCH v4 10/12] sched/fair: Select an energy-efficient CPU on task wake-up Quentin Perret
2018-06-28 11:40 ` [RFC PATCH v4 11/12] OPTIONAL: arch_topology: Start Energy Aware Scheduling Quentin Perret
2018-06-28 11:40 ` [RFC PATCH v4 12/12] OPTIONAL: cpufreq: dt: Register an Energy Model Quentin Perret
2018-07-06 10:10   ` Vincent Guittot
2018-07-06 10:18     ` Quentin Perret
2018-07-30 15:53       ` Vincent Guittot
2018-07-30 16:20         ` Quentin Perret

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