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From: Quentin Perret <quentin.perret@arm.com>
To: skannan@codeaurora.org
Cc: peterz@infradead.org, 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,
	linux-pm-owner@vger.kernel.org
Subject: Re: [PATCH v5 10/14] sched/cpufreq: Refactor the utilization aggregation method
Date: Tue, 31 Jul 2018 08:59:53 +0100
Message-ID: <20180731075950.tfvxef6yuja3ad2k@queper01-lin> (raw)
In-Reply-To: <331552975e858911db66bc78c2c8e720@codeaurora.org>

On Monday 30 Jul 2018 at 12:35:27 (-0700), skannan@codeaurora.org wrote:
[...]
> If it's going to be a different aggregation from what's done for frequency
> guidance, I don't see the point of having this inside schedutil. Why not
> keep it inside the scheduler files?

This code basically results from a discussion we had with Peter on v4.
Keeping everything centralized can make sense from a maintenance
perspective, I think. That makes it easy to see the impact of any change
to utilization signals for both EAS and schedutil.


> Also, it seems weird to use a governor's
> code when it might not actually be in use. What if someone is using
> ondemand, conservative, performance, etc?

Yeah I thought about that too ... I would say that even if you don't
use schedutil, it is probably a fair assumption from the scheduler's
standpoint to assume that somewhat OPPs follow utilization (in a very
loose way). So yes, if you use ondemand with EAS you won't have a
perfectly consistent match between the frequency requests and what EAS
predicts, and that might result in sub-optimal decisions in some cases,
but I'm not sure if we can do anything better at this stage.

Also, if you do use schedutil, EAS will accurately predict what will be
the frequency _request_, but that gives you no guarantee whatsoever that
you'll actually get it for real (because you're throttled, or because of
thermal capping, or simply because the HW refuses it for some reason ...).

There will be inconsistencies between EAS' predictions and the actual
frequencies, and we have to live with that. The best we can do is make
sure we're at least internally consistent from the scheduler's
standpoint, and that's why I think it can make sense to factorize as
many things as possible with schedutil where applicable.

> > +	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);
> > +	}
> 
> Instead of all this indentation, can't you just return early without doing
> the code inside the if?

But then I'll need to duplicate the 'min' below, so not sure if it's
worth it ?

> > +enum schedutil_type {
> > +	frequency_util,
> > +	energy_util,
> > +};
> 
> Please don't use lower case for enums. It's extremely confusing.

Ok, I'll change that in v6.

Thanks !
Quentin

  reply index

Thread overview: 72+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-24 12:25 [PATCH v5 00/14] Energy Aware Scheduling Quentin Perret
2018-07-24 12:25 ` [PATCH v5 01/14] sched: Relocate arch_scale_cpu_capacity Quentin Perret
2018-07-24 12:25 ` [PATCH v5 02/14] sched/cpufreq: Factor out utilization to frequency mapping Quentin Perret
2018-07-24 12:25 ` [PATCH v5 03/14] PM: Introduce an Energy Model management framework Quentin Perret
2018-08-09 21:52   ` Rafael J. Wysocki
2018-08-10  8:15     ` Quentin Perret
2018-08-10  8:41       ` Rafael J. Wysocki
2018-08-10  9:12         ` Quentin Perret
2018-08-10 11:13           ` Rafael J. Wysocki
2018-08-10 12:30             ` Quentin Perret
2018-08-12  9:49               ` Rafael J. Wysocki
2018-07-24 12:25 ` [PATCH v5 04/14] PM / EM: Expose the Energy Model in sysfs Quentin Perret
2018-07-24 12:25 ` [PATCH v5 05/14] sched/topology: Reference the Energy Model of CPUs when available Quentin Perret
2018-07-24 12:25 ` [PATCH v5 06/14] sched/topology: Lowest energy aware balancing sched_domain level pointer Quentin Perret
2018-07-26 16:00   ` Valentin Schneider
2018-07-26 17:01     ` Quentin Perret
2018-07-24 12:25 ` [PATCH v5 07/14] sched/topology: Introduce sched_energy_present static key Quentin Perret
2018-07-24 12:25 ` [PATCH v5 08/14] sched/fair: Clean-up update_sg_lb_stats parameters Quentin Perret
2018-07-24 12:25 ` [PATCH v5 09/14] sched: Add over-utilization/tipping point indicator Quentin Perret
2018-08-02 12:26   ` Peter Zijlstra
2018-08-02 13:03     ` Quentin Perret
2018-08-02 13:08       ` Peter Zijlstra
2018-08-02 13:18         ` Quentin Perret
2018-08-02 13:48           ` Vincent Guittot
2018-08-02 14:14             ` Quentin Perret
2018-08-02 15:14               ` Vincent Guittot
2018-08-02 15:30                 ` Quentin Perret
2018-08-02 15:55                   ` Vincent Guittot
2018-08-02 16:00                     ` Quentin Perret
2018-08-02 16:07                       ` Vincent Guittot
2018-08-02 16:10                         ` Quentin Perret
2018-08-02 16:38                           ` Vincent Guittot
2018-08-02 16:59                             ` Quentin Perret
2018-08-03  7:48                               ` Vincent Guittot
2018-08-03  8:18                                 ` Quentin Perret
2018-08-03 13:49                                   ` Vincent Guittot
2018-08-03 14:21                                     ` Vincent Guittot
2018-08-03 15:55                                     ` Quentin Perret
2018-08-06  8:40                                       ` Vincent Guittot
2018-08-06  9:43                                         ` Quentin Perret
2018-08-06 10:45                                           ` Vincent Guittot
2018-08-06 11:02                                             ` Quentin Perret
2018-08-06 10:08                                         ` Dietmar Eggemann
2018-08-06 10:33                                           ` Vincent Guittot
2018-08-06 12:29                                             ` Dietmar Eggemann
2018-08-06 12:37                                               ` Vincent Guittot
2018-08-06 13:20                                                 ` Dietmar Eggemann
2018-08-09  9:30   ` Vincent Guittot
2018-08-09  9:38     ` Quentin Perret
2018-07-24 12:25 ` [PATCH v5 10/14] sched/cpufreq: Refactor the utilization aggregation method Quentin Perret
2018-07-30 19:35   ` skannan
2018-07-31  7:59     ` Quentin Perret [this message]
2018-07-31 19:31       ` skannan
2018-08-01  7:32         ` Rafael J. Wysocki
2018-08-01  8:23           ` Quentin Perret
2018-08-01  8:35             ` Rafael J. Wysocki
2018-08-01  9:23               ` Quentin Perret
2018-08-01  9:40                 ` Rafael J. Wysocki
2018-08-02 13:04                 ` Peter Zijlstra
2018-08-02 15:39                   ` Quentin Perret
2018-08-03 13:04                     ` Quentin Perret
2018-08-02 12:33     ` Peter Zijlstra
2018-08-02 12:45       ` Peter Zijlstra
2018-08-02 15:21         ` Quentin Perret
2018-08-02 17:36           ` Peter Zijlstra
2018-08-03 12:42             ` Quentin Perret
2018-07-24 12:25 ` [PATCH v5 11/14] sched/fair: Introduce an energy estimation helper function Quentin Perret
2018-07-24 12:25 ` [PATCH v5 12/14] sched/fair: Select an energy-efficient CPU on task wake-up Quentin Perret
2018-08-02 13:54   ` Peter Zijlstra
2018-08-02 16:21     ` Quentin Perret
2018-07-24 12:25 ` [PATCH v5 13/14] OPTIONAL: arch_topology: Start Energy Aware Scheduling Quentin Perret
2018-07-24 12:25 ` [PATCH v5 14/14] OPTIONAL: cpufreq: dt: Register an Energy Model Quentin Perret

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