linux-kernel - Re: [PATCH V14 0/7] amd-pstate preferred core

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Date: Mon, 29 Jan 2024 16:18:02 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Meng Li <li.meng@....com>, Borislav Petkov <bpetkov@....com>
Cc: "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>, Huang Rui <ray.huang@....com>, 
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org, 
	linux-acpi@...r.kernel.org, Shuah Khan <skhan@...uxfoundation.org>, 
	linux-kselftest@...r.kernel.org, Nathan Fontenot <nathan.fontenot@....com>, 
	Deepak Sharma <deepak.sharma@....com>, Alex Deucher <alexander.deucher@....com>, 
	Mario Limonciello <mario.limonciello@....com>, Shimmer Huang <shimmer.huang@....com>, 
	Perry Yuan <Perry.Yuan@....com>, Xiaojian Du <Xiaojian.Du@....com>, 
	Viresh Kumar <viresh.kumar@...aro.org>, Borislav Petkov <bp@...en8.de>, 
	Oleksandr Natalenko <oleksandr@...alenko.name>
Subject: Re: [PATCH V14 0/7] amd-pstate preferred core

On Fri, Jan 19, 2024 at 10:05 AM Meng Li <li.meng@....com> wrote:
>
> Hi all:
>
> The core frequency is subjected to the process variation in semiconductors.
> 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 reach
> maximum frequency. To find the best process scheduling policy for a given
> scenario, OS needs to know the core ordering informed by the platform through
> highest performance capability register of the CPPC interface.
>
> Earlier implementations of amd-pstate preferred core only support a static
> core ranking and targeted performance. Now it has the ability to dynamically
> change the preferred core based on the workload and platform conditions and
> 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 cores
> 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-pstate
> 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?