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From: Viresh Kumar <viresh.kumar@linaro.org>
To: Nicola Mazzucato <nicola.mazzucato@arm.com>
Cc: devicetree@vger.kernel.org, linux-pm@vger.kernel.org,
	vireshk@kernel.org, daniel.lezcano@linaro.org, rjw@rjwysocki.net,
	linux-kernel@vger.kernel.org, robh+dt@kernel.org,
	sudeep.holla@arm.com, chris.redpath@arm.com,
	morten.rasmussen@arm.com, 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 16:32:41 +0530	[thread overview]
Message-ID: <20201008110241.dcyxdtqqj7slwmnc@vireshk-i7> (raw)
In-Reply-To: <2417d7b5-bc58-fa30-192c-e5991ec22ce0@arm.com>

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.

> This performance dependency information is essential for some
> components that take information from the cpufreq policy.
> 
> To restore functionality we can use the optional node
> 'cpu-performance-dependencies' in dt which will provide such dependency
> information and we can add a new cpumask 'dependency_cpus' in policy.
> 
> Hope it gives some clarity.

Some, but I am still confused :(

Can you give a real example, with exact number of CPUs, how they share
clocks/voltage domains and what else the firmware needs in terms of
performance-domains ? That may make it easier for me to understand it.

-- 
viresh

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  reply	other threads:[~2020-10-08 11:04 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 [this message]
2020-10-08 15:03         ` Ionela Voinescu
2020-10-08 15:57           ` Rafael J. Wysocki
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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