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From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Quentin Perret <quentin.perret@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux PM <linux-pm@vger.kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Ingo Molnar <mingo@redhat.com>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Morten Rasmussen <morten.rasmussen@arm.com>,
	Chris Redpath <chris.redpath@arm.com>,
	Patrick Bellasi <patrick.bellasi@arm.com>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Thara Gopinath <thara.gopinath@linaro.org>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Todd Kjos <tkjos@google.com>,
	Joel Fernandes <joel@joelfernandes.org>,
	Steve Muckle <smuckle@google.com>,
	adharmap@codeaurora.org, Saravana Kannan <skannan@codeaurora.org>,
	Pavan Kondeti <pkondeti@codeaurora.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Eduardo Valentin <edubezval@gmail.com>,
	Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
	currojerez@riseup.net, Javi Merino <javi.merino@kernel.org>
Subject: Re: [PATCH v6 13/14] sched/topology: Make Energy Aware Scheduling depend on schedutil
Date: Thu, 6 Sep 2018 11:18:55 +0200	[thread overview]
Message-ID: <CAJZ5v0jL_k36RPc6e8yUHxAYGXp7HHWK+hLnBZWnu5Oi__7j3w@mail.gmail.com> (raw)
In-Reply-To: <20180904105906.t5i7twyyt2omc45b@queper01-lin>

On Tue, Sep 4, 2018 at 12:59 PM Quentin Perret <quentin.perret@arm.com> wrote:
>
> On Monday 20 Aug 2018 at 10:44:19 (+0100), Quentin Perret wrote:
> > Energy Aware Scheduling (EAS) is designed with the assumption that
> > frequencies of CPUs follow their utilization value. When using a CPUFreq
> > governor other than schedutil, the chances of this assumption being true
> > are small, if any. When schedutil is being used, EAS' predictions are at
> > least consistent with the frequency requests. Although those requests
> > have no guarantees to be honored by the hardware, they should at least
> > guide DVFS in the right direction and provide some hope in regards to the
> > EAS model being accurate.
> >
> > To make sure EAS is only used in a sane configuration, create a strong
> > dependency on schedutil being used. Since having sugov compiled-in does
> > not provide that guarantee, extend the existing CPUFreq policy notifier
> > with a new case on governor changes. That allows the scheduler to
> > register a callback on this notifier to rebuild the scheduling domains
> > when governors are changed, and enable/disable EAS accordingly.
> >
> > cc: Ingo Molnar <mingo@redhat.com>
> > cc: Peter Zijlstra <peterz@infradead.org>
> > Signed-off-by: Quentin Perret <quentin.perret@arm.com>
> >
> > ---
> > This patch could probably be squashed into another one, but I kept it
> > separate to ease the review. Also, it's probably optional as not having
> > it will not 'break' things per se.
> >
> > I went for the smallest possible solution I could find, which has the
> > good side of being simple, but it's definitely not the only one.
> >
> > Another possibility would be to hook things in sugov_start() and
> > sugov_stop(), but that requires some more work. In this case, it
> > wouldn't be possible to just re-build the sched_domains() from there,
> > because when sugov_stop() is called, the 'governor' field of the policy
> > hasn't been updated yet, so the condition (if gov == schedutil) in
> > build_freq_domains() doesn't work.
> >
> > To workaround the issue we'll need to find a way to pass a cpumask to
> > the topology code to specifically say 'sugov has been stopped on these
> > CPUs'. That would mean more code to handle that, but that would also
> > mean we don't have to mess around with the CPUFreq notifiers ...
> >
> > Not sure what's best, so all feedback is more than welcome.
>
> Hi,
>
> Does anybody have concerns with this patch ? Is it a reasonable option
> to use the CPUFreq notifiers in this case ? If there is anything I can
> do to ease the review please let me know.

I'm not a particular fan of notifiers to be honest and you don't need
to add an extra chain just in order to be able to register a callback
from a single user.  That can be achieved with a single callback
pointer too, but also you could just call a function exported by the
scheduler directly from where in the cpufreq code it needs to be
called.

> Also, is there any hope that the 12 first patches could make it in 4.20
> on their own ? Or is it already too late ?

I'm walking through them right now, albeit somewhat slowly due to
various distractions, so we'll see.

Thanks,
Rafael

  reply	other threads:[~2018-09-06  9:19 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-20  9:44 [PATCH v6 00/14] Energy Aware Scheduling Quentin Perret
2018-08-20  9:44 ` [PATCH v6 01/14] sched: Relocate arch_scale_cpu_capacity Quentin Perret
2018-08-20  9:44 ` [PATCH v6 02/14] sched/cpufreq: Factor out utilization to frequency mapping Quentin Perret
2018-09-10  9:29   ` Rafael J. Wysocki
2018-08-20  9:44 ` [PATCH v6 03/14] PM: Introduce an Energy Model management framework Quentin Perret
2018-08-29 10:04   ` Patrick Bellasi
2018-08-29 13:28     ` Quentin Perret
2018-08-31  9:04       ` Patrick Bellasi
2018-09-11  9:34       ` Andrea Parri
2018-09-11 12:32         ` Quentin Perret
2018-09-11 13:31           ` Andrea Parri
2018-09-10  9:44   ` Rafael J. Wysocki
2018-09-10 10:38     ` Quentin Perret
2018-09-10 10:40       ` Rafael J. Wysocki
2018-08-20  9:44 ` [PATCH v6 04/14] PM / EM: Expose the Energy Model in sysfs Quentin Perret
2018-09-06  6:56   ` Dietmar Eggemann
2018-09-06 14:09     ` Quentin Perret
2018-09-07  0:14       ` Dietmar Eggemann
2018-08-20  9:44 ` [PATCH v6 05/14] sched/topology: Reference the Energy Model of CPUs when available Quentin Perret
2018-08-29 16:22   ` Patrick Bellasi
2018-08-29 16:56     ` Quentin Perret
2018-08-30 10:00       ` Patrick Bellasi
2018-08-30 10:47         ` Quentin Perret
2018-08-30 12:50           ` Patrick Bellasi
2018-08-20  9:44 ` [PATCH v6 06/14] sched/topology: Lowest CPU asymmetry sched_domain level pointer Quentin Perret
2018-08-20  9:44 ` [PATCH v6 07/14] sched/topology: Introduce sched_energy_present static key Quentin Perret
2018-08-29 16:50   ` Patrick Bellasi
2018-08-29 17:20     ` Quentin Perret
2018-08-30  9:23       ` Patrick Bellasi
2018-08-30  9:57         ` Quentin Perret
2018-08-30 10:18           ` Patrick Bellasi
2018-09-06  6:06   ` Dietmar Eggemann
2018-09-06  9:29     ` Quentin Perret
2018-09-06 23:49       ` Dietmar Eggemann
2018-09-07  8:24         ` Quentin Perret
2018-08-20  9:44 ` [PATCH v6 08/14] sched/fair: Clean-up update_sg_lb_stats parameters Quentin Perret
2018-08-20  9:44 ` [PATCH v6 09/14] sched: Add over-utilization/tipping point indicator Quentin Perret
2018-08-20  9:44 ` [PATCH v6 10/14] sched/cpufreq: Refactor the utilization aggregation method Quentin Perret
2018-09-10  9:53   ` Rafael J. Wysocki
2018-09-10 10:07     ` Quentin Perret
2018-09-10 10:25       ` Rafael J. Wysocki
2018-08-20  9:44 ` [PATCH v6 11/14] sched/fair: Introduce an energy estimation helper function Quentin Perret
2018-08-20  9:44 ` [PATCH v6 12/14] sched/fair: Select an energy-efficient CPU on task wake-up Quentin Perret
2018-08-20  9:44 ` [PATCH v6 13/14] sched/topology: Make Energy Aware Scheduling depend on schedutil Quentin Perret
2018-09-04 10:59   ` Quentin Perret
2018-09-06  9:18     ` Rafael J. Wysocki [this message]
2018-09-06 14:38       ` Quentin Perret
2018-09-07  8:52         ` Rafael J. Wysocki
2018-09-07  8:56           ` Rafael J. Wysocki
2018-09-07  9:02             ` Quentin Perret
2018-09-07 15:29           ` Quentin Perret
2018-09-09 20:13             ` Rafael J. Wysocki
2018-09-10  8:24               ` Quentin Perret
2018-09-10  8:55                 ` Rafael J. Wysocki
2018-09-10  9:43                   ` Quentin Perret
2018-08-20  9:44 ` [PATCH v6 14/14] OPTIONAL: cpufreq: dt: Register an Energy Model Quentin Perret
2018-09-10  9:12 ` [PATCH v6 00/14] Energy Aware Scheduling Rafael J. Wysocki

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