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From: Quentin Perret <quentin.perret@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
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@codeaurora.org, skannan@codeaurora.org,
	pkondeti@codeaurora.org, juri.lelli@redhat.com,
	edubezval@gmail.com, srinivas.pandruvada@linux.intel.com,
	currojerez@riseup.net, javi.merino@kernel.org
Subject: Re: [PATCH v7 13/14] sched/topology: Make Energy Aware Scheduling depend on schedutil
Date: Thu, 4 Oct 2018 12:58:41 +0100	[thread overview]
Message-ID: <20181004115839.c5g2fsehszbvwoqq@queper01-lin> (raw)
In-Reply-To: <20181004105023.GE19252@hirez.programming.kicks-ass.net>

On Thursday 04 Oct 2018 at 12:50:23 (+0200), Peter Zijlstra wrote:
> On Wed, Sep 12, 2018 at 10:13:08AM +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, make CPUFreq call a scheduler function on
> > on governor changes hence letting it rebuild the scheduling domains,
> > check the governors of the online CPUs, and enable/disable EAS
> > accordingly.
> 
> So this patch disables EAS when we change cpufreq gov. How about we
> force select schedutil and disallow changing it when EAS is enabled?
> 
> Instead of silently disabling EAS when we frob the governor?

By doing it this way I think we have a better integration with things
like that exclusive cpusets. In the end, EAS is enabled in a
per-root_domain basis. So, say you have two root domains, A and B. EAS
is enabled on A and disabled on B (because it doesn't have
SD_ASYM_CPUCAPACITY or something). Should you be forced to use sugov on
the CPUs of B to run EAS on A ? If there is a cpufreq policy covering
only the CPUs of B, I'd say probably no.

Now I get the argument that this is happening silently as-is, so we can
do better. How about we put a message in dmesg we EAS gets disabled in
case of governor changes ?

Also, I'm currently working on a doc patch for EAS ATM (to be posted
soon), so I can (and will) make it very clear there that you _must_
use sugov to use EAS.

Would that work ?

Thanks,
Quentin

  reply	other threads:[~2018-10-04 11:58 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-12  9:12 [PATCH v7 00/14] Energy Aware Scheduling Quentin Perret
2018-09-12  9:12 ` [PATCH v7 01/14] sched: Relocate arch_scale_cpu_capacity Quentin Perret
2018-09-12  9:12 ` [PATCH v7 02/14] sched/cpufreq: Prepare schedutil for Energy Aware Scheduling Quentin Perret
2018-09-12 14:56   ` Vincent Guittot
2018-09-18 21:33   ` Rafael J. Wysocki
2018-09-27 12:17     ` Quentin Perret
2018-09-28  8:23       ` Rafael J. Wysocki
2018-09-28  8:35         ` Quentin Perret
2018-09-28  8:35           ` Rafael J. Wysocki
2018-09-12  9:12 ` [PATCH v7 03/14] PM: Introduce an Energy Model management framework Quentin Perret
2018-10-02 12:25   ` Peter Zijlstra
2018-10-02 12:54     ` Quentin Perret
2018-10-02 13:50       ` Peter Zijlstra
2018-10-02 12:30   ` Peter Zijlstra
2018-10-02 12:51     ` Quentin Perret
2018-10-02 13:48       ` Peter Zijlstra
2018-10-02 14:05         ` Quentin Perret
2018-10-02 14:29           ` Peter Zijlstra
2018-10-02 14:40             ` Quentin Perret
2018-10-02 19:12               ` Andrea Parri
2018-10-03  7:48                 ` Quentin Perret
2018-09-12  9:12 ` [PATCH v7 04/14] PM / EM: Expose the Energy Model in sysfs Quentin Perret
2018-09-12  9:13 ` [PATCH v7 05/14] sched: Introduce a sched_feat for Energy Aware Scheduling Quentin Perret
2018-10-02 12:34   ` Peter Zijlstra
2018-10-02 13:08     ` Quentin Perret
2018-10-03 16:24       ` Peter Zijlstra
2018-10-04  9:57         ` Quentin Perret
2018-09-12  9:13 ` [PATCH v7 06/14] sched/topology: Reference the Energy Model of CPUs when available Quentin Perret
2018-10-02 12:36   ` Peter Zijlstra
2018-10-02 13:16     ` Quentin Perret
2018-09-12  9:13 ` [PATCH v7 07/14] sched/topology: Lowest CPU asymmetry sched_domain level pointer Quentin Perret
2018-09-12  9:13 ` [PATCH v7 08/14] sched/topology: Disable EAS on inappropriate platforms Quentin Perret
2018-10-03 16:27   ` Peter Zijlstra
2018-10-04  9:10     ` Quentin Perret
2018-10-04  9:38       ` Peter Zijlstra
2018-10-04  9:45         ` Quentin Perret
2018-09-12  9:13 ` [PATCH v7 09/14] sched/fair: Clean-up update_sg_lb_stats parameters Quentin Perret
2018-09-12  9:13 ` [PATCH v7 10/14] sched: Add over-utilization/tipping point indicator Quentin Perret
2018-09-12  9:13 ` [PATCH v7 11/14] sched/fair: Introduce an energy estimation helper function Quentin Perret
2018-10-04  8:34   ` Peter Zijlstra
2018-10-04  9:02     ` Quentin Perret
2018-09-12  9:13 ` [PATCH v7 12/14] sched/fair: Select an energy-efficient CPU on task wake-up Quentin Perret
2018-10-04  9:44   ` Peter Zijlstra
2018-10-04 10:27     ` Quentin Perret
2018-10-04 10:41       ` Peter Zijlstra
2018-10-04 10:55         ` Quentin Perret
2018-10-04 12:18           ` Peter Zijlstra
2018-09-12  9:13 ` [PATCH v7 13/14] sched/topology: Make Energy Aware Scheduling depend on schedutil Quentin Perret
2018-10-04 10:50   ` Peter Zijlstra
2018-10-04 11:58     ` Quentin Perret [this message]
2018-09-12  9:13 ` [PATCH v7 14/14] OPTIONAL: cpufreq: dt: Register an Energy Model Quentin Perret

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