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From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Quentin Perret <quentin.perret@arm.com>
Cc: peterz@infradead.org, 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: [PATCH v5 03/14] PM: Introduce an Energy Model management framework
Date: Fri, 10 Aug 2018 13:13:22 +0200
Message-ID: <8482157.ZqyaK8WryI@aspire.rjw.lan> (raw)
In-Reply-To: <20180810091216.nieosjtu7l33z4ap@queper01-lin>

On Friday, August 10, 2018 11:12:18 AM CEST Quentin Perret wrote:
> On Friday 10 Aug 2018 at 10:41:56 (+0200), Rafael J. Wysocki wrote:
> > On Friday, August 10, 2018 10:15:39 AM CEST Quentin Perret wrote:

[cut]

> Agreed. EAS and IPA don't care about the absolute real power values, all
> they care about is relative correctness. But what I really want to avoid
> is having IPA getting the power of the GPUs in mW, and the power of CPUs
> in an abstract scale without unit. That _will_ create problems eventually
> IMO, because the behaviour is undefined. Specifying a unit everywhere is
> an easy way to enforce a consistent design across sub-systems, that's
> all.

OK

> > > What I am currently proposing is to keep the unit (mW) in the EM
> > > framework so that migrating IPA to using it can be done in a (relatively)
> > > painless way. On a system where drivers  don't know the exact wattage,
> > > then they should just 'lie' to the EM framework, but it's their job to
> > > lie coherently to all subsystems and keep things consistent, because all
> > > subsystems have specified power in comparable units.
> > 
> > Alternatively, there could be a translation layer between EM and IPA.
> 
> Hmm, interesting... What do you have in mind exactly ? What would you
> put in that layer ?

Something able to say how the numbers used by EM and IPA are related. :-)

Do you think that IPA and EM will always need to use the same set of data for
the CPU?

> > From my experience, if you want people to come up with some numbers,
> > they will just choose them to game the system this way or another
> > unless those numbers can be measured directly or are clearly documented.
> > 
> > And if that happens and then you want to make any significant changes,
> > you'll need to deal with "regressions" occuring because someone chose
> > the numbers to make the system behave in a specific way and your changes
> > break that.
> > 
> > As a rule, I rather avoid requesting unknown numbers from people. :-)
> > 
> > > Another solution to solve this problem could be to extend the EM
> > > framework introduced by this patch and make it manage the EM of any
> > > device, not just CPUs. Then we could just specify that all power costs
> > > must be in the same scale, regardless of the actual unit, and register
> > > the EM of CPUs, GPUs, ...
> > > However, I was hoping that this patch as-is was enough for a first step,
> > > and that this extension of the framework could be done in a second step ?
> > > Thoughts ?
> > > 
> > > In any case, if we decide to keep the mW unit for now, I should at least
> > > explain clearly why in the commit message.
> > 
> > Right.
> > 
> > Actually, the unit is as good as any other, but you need to bear in mind that
> > the numbers provided may not be realistic.
> 
> As long as they're all correct in a relative way, that's fine by me :-)

OK

Thanks,
Rafael


  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 [this message]
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
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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