From: Quentin Perret <qperret@google.com>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>,
Lukasz Luba <lukasz.luba@arm.com>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux PM <linux-pm@vger.kernel.org>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
Rob Herring <robh+dt@kernel.org>,
Amit Kucheria <amitk@kernel.org>,
Jonathan Corbet <corbet@lwn.net>,
Dietmar Eggemann <Dietmar.Eggemann@arm.com>,
Doug Anderson <dianders@chromium.org>,
Matthias Kaehlcke <mka@chromium.org>,
"Nayak, Rajendra" <rnayak@codeaurora.org>
Subject: Re: [PATCH v2 0/3] Clarify abstract scale usage for power values in Energy Model, EAS and IPA
Date: Thu, 15 Oct 2020 16:04:11 +0100 [thread overview]
Message-ID: <20201015150411.GA1859176@google.com> (raw)
In-Reply-To: <CAJZ5v0hV8fwRnADdjiiF=zapO3AE6=_W_PeOQ_WhUirCcFkgdA@mail.gmail.com>
On Thursday 15 Oct 2020 at 15:40:16 (+0200), Rafael J. Wysocki wrote:
> On Thu, Oct 15, 2020 at 12:22 PM Daniel Lezcano
> <daniel.lezcano@linaro.org> wrote:
> >
> > On 15/10/2020 11:00, Lukasz Luba wrote:
> >
> > [ ... ]
> >
> > >> There is the SCMI and the DT. Because there are two sources where it is
> > >> impossible to know if they are using the same units, we are stuck to
> > >> ensure a consistency for the kernel.
> > >>
> > >> The platform should use:
> > >> - the SCMI only (scaled or real)
> > >> - the DT only (real)
> > >> [ - the firmware file only (scaled or real) ]
> > >>
> > >
> > > Do you mean by SCMI - registration using em_dev_register_perf_domain() ?
> >
> > It was high level description, but yes, I guess it is the case.
> >
> > >> As it is not possible to know if they are scaled or real, there is no
> > >> choice except making them mutually exclusive.
> > >
> > > So you propose a bit more restriction in registration EM, to not get
> > > lost in the future. I also have these doubts. Let's consider it and
> > > maybe agree.
> > >
> > > I've recommended Qcom to use em_dev_register_perf_domain() when they
> > > have this obfuscated power values. Then any developer in the future
> > > who wants to add EM for a new device on that platform, should use the
> > > em_dev_register_perf_domain().
> > >
> > > In this case the flag in EM that you have proposed makes sense.
> > > We probably need an argument 'bool abstract_scale' in the
> > > em_dev_register_perf_domain(..., bool abstract_scale)
> > > as a source of information.
> >
> > I was suggesting to add a flag to the em_perf_domain structure giving
> > the source of the power numbers.
> >
> > So if the IPA is having the 'sustainable-power' set in DT but the
> > em_perf_domain is flagged with power number coming from SCMI, then they
> > will be incompatible, the thermal zone will fail to register.
> >
> >
> > > We would allow to co-exist em_dev_register_perf_domain(..., false)
> > > with dev_pm_opp_of_register_em() EM devices.
> > >
> > > Is it make sense?
> >
> > Well, it does not change my opinion. We should assume the energy model
> > is always milliwatts. If the SoC vendors find a way to get around with
> > bogoWatts, then good to them and up to them to deal with in the future.
>
> That sounds fair enough, but it also means that any kernel patches
> using power units different from milliwatts for the EM should be
> rejected in the future, doesn't it?
>
> And the existing code using different power units for the EM (if any)
> should be updated/fixed accordingly, shouldn't it?
>
> Otherwise I don't see now this can be regarded as a hard rule.
Sorry, jumping late in the discussion :)
To add a bit of background to this, it's been the plan from the very
beginning to make PM_EM use an abstract scale. The only reason it was
not merged like that is because the first version only worked for CPUs,
and IPA was using a totally different source for other devices. So we
had no choice but to specify PM_EM in mW to keep things compatible and
allow to transition IPA. But that is no longer true, so I'm in favor of
evolving PM_EM where it was supposed to be to begin with.
IMO, the only thing the kernel cares about is consistency across power
numbers, but not about the exact unit. And I agree with Rafael, we have
code paths in the kernel that feed data in PM_EM but _cannot_ guarantee
mW, SCMI being a prime example, so I don't think it is reasonable to
mandate that.
Having that properly documented + an 'abstract_scale' parameter in
dev_pm_opp_of_register_em() (or even a unit, which could be bogo-watts)
should work IMO. What is the concern with this approach?
Thanks,
Quentin
next prev parent reply other threads:[~2020-10-15 15:04 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-02 11:44 [PATCH v2 0/3] Clarify abstract scale usage for power values in Energy Model, EAS and IPA Lukasz Luba
2020-10-02 11:44 ` [PATCH v2 1/3] docs: Clarify abstract scale usage for power values in Energy Model Lukasz Luba
2020-10-02 11:44 ` [PATCH v2 2/3] PM / EM: update the comments related to power scale Lukasz Luba
2020-10-02 11:44 ` [PATCH v2 3/3] dt-bindings: thermal: update sustainable-power with abstract scale Lukasz Luba
2020-10-02 14:31 ` Doug Anderson
2020-10-02 15:12 ` Lukasz Luba
2020-10-02 15:47 ` Doug Anderson
2020-10-02 16:40 ` Lukasz Luba
2020-10-02 17:39 ` Doug Anderson
2020-10-06 22:24 ` Rob Herring
2020-10-07 1:17 ` Doug Anderson
2020-10-07 13:26 ` Rob Herring
2020-10-07 21:40 ` Doug Anderson
2020-10-08 14:20 ` Lukasz Luba
2020-10-08 16:41 ` Doug Anderson
2020-10-07 9:03 ` Lukasz Luba
2020-10-05 13:58 ` Rob Herring
2020-10-05 16:14 ` Lukasz Luba
2020-10-09 9:16 ` [PATCH v2 0/3] Clarify abstract scale usage for power values in Energy Model, EAS and IPA Lukasz Luba
2020-10-14 8:22 ` Daniel Lezcano
2020-10-14 9:08 ` Lukasz Luba
2020-10-14 11:23 ` Daniel Lezcano
2020-10-14 15:24 ` Lukasz Luba
2020-10-14 17:10 ` Daniel Lezcano
2020-10-15 9:00 ` Lukasz Luba
2020-10-15 10:21 ` Daniel Lezcano
2020-10-15 13:40 ` Rafael J. Wysocki
2020-10-15 15:04 ` Quentin Perret [this message]
2020-10-16 11:48 ` Daniel Lezcano
2020-10-16 12:18 ` Quentin Perret
2020-10-16 12:50 ` Daniel Lezcano
2020-10-16 13:09 ` Quentin Perret
2020-10-16 14:36 ` Doug Anderson
2020-10-16 15:55 ` Quentin Perret
2020-10-16 14:42 ` Lukasz Luba
2020-10-16 16:02 ` Quentin Perret
2020-10-19 10:35 ` Lukasz Luba
2020-10-15 13:33 ` Rafael J. Wysocki
2020-10-15 13:39 ` Daniel Lezcano
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