LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Quentin Perret <quentin.perret@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: skannan@codeaurora.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: Thu, 2 Aug 2018 16:21:11 +0100
Message-ID: <20180802152109.2k45jqbfquef6u62@queper01-lin> (raw)
In-Reply-To: <20180802124511.GN2512@hirez.programming.kicks-ass.net>

On Thursday 02 Aug 2018 at 14:45:11 (+0200), Peter Zijlstra wrote:
> On Thu, Aug 02, 2018 at 02:33:15PM +0200, Peter Zijlstra wrote:
> > On Mon, Jul 30, 2018 at 12:35:27PM -0700, skannan@codeaurora.org wrote:
> > > On 2018-07-24 05:25, Quentin Perret 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? 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?
> > 
> > EAS hard relies on schedutil -- I suppose we need a check for that
> > somewhere and maybe some infrastructure to pin the cpufreq governor.
> 
> Either that or disable EAS when another governor is selected.
> 
> > We're simply not going to support it for anything else.
> 
> To clarify, it makes absolutely no sense what so ever to attempt EAS
> when the DVFS control is not coordinated.

I tend to agree with that, but at the same time even if we create a very
strong dependency on schedutil, we will have no guarantee that the actual
frequencies used on the platform are the ones we predicted in EAS.

There are a number of reasons why a frequency request might not be served
(throttling, thermal capping, something HW-related, ...), so it's hard
to enforce the EAS model in practice.

The way I see things, EAS needs to assume that OPPs follow utilization.
Sugov does something that looks like that too, and it's also in the
scheduler, so that makes sense to try and factorize things, especially
for maintenance purpose. But I feel like the correlation between the two
could stop here.

If you use some sort HW governor that tries to always have some idle time
on the CPUs, then the assumption that OPPs follow utilization isn't _totally_
wrong. There should be a (loose) relation between what EAS 'thinks'
and the reality. And if this isn't true, then you might make slightly
sub-optimal decisions, but I'm not sure if there is anything we can do
about it :/

The scheduler works with various models which, by definition, don't
always perfectly reflect the reality. But those models are useful
because they enable us to reason about things and make decisions. EAS uses
a model where OPPs follow utilization. I think it's just another model
to the list, and we can't really enforce it strictly in practice anyway,
so we will have to live with its inaccuracies I suppose ...

I hope that makes sense :-)

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
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 [this message]
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

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20180802152109.2k45jqbfquef6u62@queper01-lin \
    --to=quentin.perret@arm.com \
    --cc=adharmap@quicinc.com \
    --cc=chris.redpath@arm.com \
    --cc=currojerez@riseup.net \
    --cc=dietmar.eggemann@arm.com \
    --cc=edubezval@gmail.com \
    --cc=gregkh@linuxfoundation.org \
    --cc=javi.merino@kernel.org \
    --cc=joel@joelfernandes.org \
    --cc=juri.lelli@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-pm-owner@vger.kernel.org \
    --cc=linux-pm@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=morten.rasmussen@arm.com \
    --cc=patrick.bellasi@arm.com \
    --cc=peterz@infradead.org \
    --cc=pkondeti@codeaurora.org \
    --cc=rjw@rjwysocki.net \
    --cc=skannan@codeaurora.org \
    --cc=skannan@quicinc.com \
    --cc=smuckle@google.com \
    --cc=srinivas.pandruvada@linux.intel.com \
    --cc=thara.gopinath@linaro.org \
    --cc=tkjos@google.com \
    --cc=valentin.schneider@arm.com \
    --cc=vincent.guittot@linaro.org \
    --cc=viresh.kumar@linaro.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org linux-kernel@archiver.kernel.org
	public-inbox-index lkml


Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/ public-inbox