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Message-ID: <d21b3514-76f0-4571-b904-7b6f3e536328@arm.com>
Date:   Tue, 12 Dec 2023 19:51:41 +0100
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Subject: Re: [PATCH v5 23/23] Documentation: EM: Update with runtime
 modification design
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To:     Lukasz Luba <lukasz.luba@arm.com>, linux-kernel@vger.kernel.org,
        linux-pm@vger.kernel.org, rafael@kernel.org
Cc:     rui.zhang@intel.com, amit.kucheria@verdurent.com,
        amit.kachhap@gmail.com, daniel.lezcano@linaro.org,
        viresh.kumar@linaro.org, len.brown@intel.com, pavel@ucw.cz,
        mhiramat@kernel.org, qyousef@layalina.io, wvw@google.com
References: <20231129110853.94344-1-lukasz.luba@arm.com>
 <20231129110853.94344-24-lukasz.luba@arm.com>
From:   Dietmar Eggemann <dietmar.eggemann@arm.com>
In-Reply-To: <20231129110853.94344-24-lukasz.luba@arm.com>
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On 29/11/2023 12:08, Lukasz Luba wrote:
> Add a new section 'Design' which covers the information about Energy
> Model. It contains the design decisions, describes models and how they
> reflect the reality. Remove description of the default EM. Change the
> other section IDs. Add documentation bit for the new feature which
> allows to modify the EM in runtime.
> 
> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
> ---
>  Documentation/power/energy-model.rst | 206 +++++++++++++++++++++++++--
>  1 file changed, 196 insertions(+), 10 deletions(-)
> 
> diff --git a/Documentation/power/energy-model.rst b/Documentation/power/energy-model.rst
> index 13225965c9a4..1f8cf36914b1 100644
> --- a/Documentation/power/energy-model.rst
> +++ b/Documentation/power/energy-model.rst
> @@ -72,16 +72,48 @@ required to have the same micro-architecture. CPUs in different performance
>  domains can have different micro-architectures.
>  
>  
> -2. Core APIs
> +2. Design
> +-----------------
> +
> +2.1 Runtime modifiable EM
> +^^^^^^^^^^^^^^^^^^^^^^^^^

The issue I see here is that since now the EM is runtime modifiable and
there is only one EM people might be confused in locking for a
non-runtime modifiable EM. (which matches the design till v4).

So 'runtime modifiability' is now feature of the EM itself.

There is also a figure in this document illustrating the use of
em_get_energy(), em_cpu_get() and em_dev_register_perf_domain().

I wonder if this should be extended to cover all the new interfaces
created for the 'runtime modifiability' feature?

[...]