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From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Ionela Voinescu <ionela.voinescu@arm.com>
Cc: "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	Sudeep Holla <sudeep.holla@arm.com>,
	Linux PM <linux-pm@vger.kernel.org>,
	Viresh Kumar <vireshk@kernel.org>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Rob Herring <robh+dt@kernel.org>,
	Nicola Mazzucato <nicola.mazzucato@arm.com>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Chris Redpath <chris.redpath@arm.com>,
	Morten Rasmussen <morten.rasmussen@arm.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v2 2/2] [RFC] CPUFreq: Add support for cpu-perf-dependencies
Date: Thu, 8 Oct 2020 17:57:23 +0200	[thread overview]
Message-ID: <CAJZ5v0j=g6y53yk_+cPNnUYb6usrQmghCNuiHYc1vbpsypFtCQ@mail.gmail.com> (raw)
In-Reply-To: <20201008150317.GB20268@arm.com>

On Thu, Oct 8, 2020 at 5:03 PM Ionela Voinescu <ionela.voinescu@arm.com> wrote:
>
> Hi Viresh,
>
> On Thursday 08 Oct 2020 at 16:32:41 (+0530), Viresh Kumar wrote:
> > On 07-10-20, 13:58, Nicola Mazzucato wrote:
> > > Hi Viresh,
> > >
> > > performance controls is what is exposed by the firmware through a protocol that
> > > is not capable of describing hardware (say SCMI). For example, the firmware can
> > > tell that the platform has N controls, but it can't say to which hardware they
> > > are "wired" to. This is done in dt, where, for example, we map these controls
> > > to cpus, gpus, etc.
> > >
> > > Let's focus on cpus.
> > >
> > > Normally we would have N of performance controls (what comes from f/w)
> > > that that correspond to hardware clock/dvfs domains.
> > >
> > > However, some firmware implementations might benefit from having finer
> > > grained information about the performance requirements (e.g.
> > > per-CPU) and therefore choose to present M performance controls to the
> > > OS. DT would be adjusted accordingly to "wire" these controls to cpus
> > > or set of cpus.
> > > In this scenario, the f/w will make aggregation decisions based on the
> > > requests it receives on these M controls.
> > >
> > > Here we would have M cpufreq policies which do not necessarily reflect the
> > > underlying clock domains, thus some s/w components will underperform
> > > (EAS and thermal, for example).
> > >
> > > A real example would be a platform in which the firmware describes the system
> > > having M per-cpu control, and the cpufreq subsystem will have M policies while
> > > in fact these cpus are "performance-dependent" each other (e.g. are in the same
> > > clock domain).
> >
> > If the CPUs are in the same clock domain, they must be part of the
> > same cpufreq policy.
>
> But cpufreq does not currently support HW_ALL (I'm using the ACPI
> coordination type to describe the generic scenario of using hardware
> aggregation and coordination when establishing the clock rate of CPUs).
>
> Adding support for HW_ALL* will involve either bypassing some
> assumptions around cpufreq policies or making core cpufreq changes.
>
> In the way I see it, support for HW_ALL involves either:
>
>  - (a) Creating per-cpu policies in order to allow each of the CPUs to
>    send their own frequency request to the hardware which will do
>    aggregation and clock rate decision at the level of the clock
>    domain.

This has been done for years on many platforms.

>    The PSD domains (ACPI) and the new DT binding will tell
>    which CPUs are actually in the same clock domain for whomever is
>    interested, despite those CPUs not being in the same policy.

And this information hasn't been used so far in those cases.

>    This requires the extra mask that Nicola introduced.

What would you use it for, specifically?

>  - (b) Making deep changes to cpufreq (core/governors/drivers) to allow:

Not an option really.

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  reply	other threads:[~2020-10-08 16:10 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-24  9:53 [PATCH v2 0/2] CPUFreq: Add support for cpu performance dependencies Nicola Mazzucato
2020-09-24  9:53 ` [PATCH v2 1/2] dt-bindings: arm: Add devicetree binding for cpu-performance-dependencies Nicola Mazzucato
2020-10-08 13:42   ` Ionela Voinescu
2020-09-24  9:53 ` [PATCH v2 2/2] [RFC] CPUFreq: Add support for cpu-perf-dependencies Nicola Mazzucato
2020-10-06  7:19   ` Viresh Kumar
2020-10-07 12:58     ` Nicola Mazzucato
2020-10-08 11:02       ` Viresh Kumar
2020-10-08 15:03         ` Ionela Voinescu
2020-10-08 15:57           ` Rafael J. Wysocki [this message]
2020-10-08 17:08             ` Ionela Voinescu
2020-10-12 16:06             ` Sudeep Holla
2020-10-08 16:00           ` Nicola Mazzucato
2020-10-09  5:39             ` Viresh Kumar
2020-10-09 11:10               ` Nicola Mazzucato
2020-10-09 11:17                 ` Viresh Kumar
2020-10-09 14:01                 ` Rob Herring
2020-10-09 15:28                   ` Nicola Mazzucato
2020-10-12  4:19                     ` Viresh Kumar
2020-10-12 10:22                   ` Lukasz Luba
2020-10-12 10:50                     ` Rafael J. Wysocki
2020-10-12 11:05                       ` Lukasz Luba
2020-10-12 10:59                     ` Ionela Voinescu
2020-10-12 13:48                       ` Lukasz Luba
2020-10-12 16:30                         ` Ionela Voinescu
2020-10-12 18:19                           ` Lukasz Luba
2020-10-12 22:01                             ` Ionela Voinescu
2020-10-13 11:53                               ` Rafael J. Wysocki
2020-10-13 12:39                                 ` Ionela Voinescu
2020-10-15 15:56                                   ` Rafael J. Wysocki
2020-10-15 18:38                                     ` Ionela Voinescu
2020-10-12 13:59                     ` Rob Herring
2020-10-12 16:02                     ` Sudeep Holla
2020-10-12 15:54                   ` Sudeep Holla
2020-10-12 15:49               ` Sudeep Holla
2020-10-12 16:52                 ` Ionela Voinescu
2020-10-12 17:18                   ` Lukasz Luba
2020-10-14  4:25                     ` Viresh Kumar
2020-10-14  9:11                       ` Lukasz Luba
2020-10-19  8:50                       ` Nicola Mazzucato
2020-10-19  9:46                         ` Viresh Kumar
2020-10-19 13:36                           ` Nicola Mazzucato
2020-10-20 10:48                             ` Viresh Kumar
2020-10-13 13:53               ` Lukasz Luba
2020-10-14  4:20                 ` Viresh Kumar

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