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From: "Rafael J. Wysocki" <rafael@kernel.org>
Date: Mon, 29 Jan 2024 16:18:02 +0100
Message-ID: <CAJZ5v0gzKdjZJBypEw1+czGN-SHbx0s0-h=Lq96+MDVAO11PYQ@mail.gmail.com>
Subject: Re: [PATCH V14 0/7] amd-pstate preferred core
To: Meng Li <li.meng@amd.com>, Borislav Petkov <bpetkov@amd.com>
Cc: "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>, Huang Rui <ray.huang@amd.com>, 
	linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, 
	linux-acpi@vger.kernel.org, Shuah Khan <skhan@linuxfoundation.org>, 
	linux-kselftest@vger.kernel.org, Nathan Fontenot <nathan.fontenot@amd.com>, 
	Deepak Sharma <deepak.sharma@amd.com>, Alex Deucher <alexander.deucher@amd.com>, 
	Mario Limonciello <mario.limonciello@amd.com>, Shimmer Huang <shimmer.huang@amd.com>, 
	Perry Yuan <Perry.Yuan@amd.com>, Xiaojian Du <Xiaojian.Du@amd.com>, 
	Viresh Kumar <viresh.kumar@linaro.org>, Borislav Petkov <bp@alien8.de>, 
	Oleksandr Natalenko <oleksandr@natalenko.name>
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On Fri, Jan 19, 2024 at 10:05=E2=80=AFAM Meng Li <li.meng@amd.com> wrote:
>
> Hi all:
>
> The core frequency is subjected to the process variation in semiconductor=
s.
> Not all cores are able to reach the maximum frequency respecting the
> infrastructure limits. Consequently, AMD has redefined the concept of
> maximum frequency of a part. This means that a fraction of cores can reac=
h
> maximum frequency. To find the best process scheduling policy for a given
> scenario, OS needs to know the core ordering informed by the platform thr=
ough
> highest performance capability register of the CPPC interface.
>
> Earlier implementations of amd-pstate preferred core only support a stati=
c
> core ranking and targeted performance. Now it has the ability to dynamica=
lly
> change the preferred core based on the workload and platform conditions a=
nd
> accounting for thermals and aging.
>
> Amd-pstate driver utilizes the functions and data structures provided by
> the ITMT architecture to enable the scheduler to favor scheduling on core=
s
> which can be get a higher frequency with lower voltage.
> We call it amd-pstate preferred core.
>
> Here sched_set_itmt_core_prio() is called to set priorities and
> sched_set_itmt_support() is called to enable ITMT feature.
> Amd-pstate driver uses the highest performance value to indicate
> the priority of CPU. The higher value has a higher priority.
>
> Amd-pstate driver will provide an initial core ordering at boot time.
> It relies on the CPPC interface to communicate the core ranking to the
> operating system and scheduler to make sure that OS is choosing the cores
> with highest performance firstly for scheduling the process. When amd-pst=
ate
> driver receives a message with the highest performance change, it will
> update the core ranking.

Hi Boris,

You've had comments on the previous version of this.

Have they all been addressed?