linux-kernel - Re: [PATCH V7 0/7] amd-pstate preferred core

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Date:   Mon, 18 Sep 2023 11:44:35 -0600
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Meng Li <li.meng@....com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Huang Rui <ray.huang@....com>
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-acpi@...r.kernel.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>,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH V7 0/7] amd-pstate preferred core

On 9/18/23 02:14, Meng Li 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.
> 
> Changes form V6->V7:
> - x86:
> - - Modify kconfig about X86_AMD_PSTATE.
> - cpufreq: amd-pstate:
> - - modify incorrect comments about scheduler_work().
> - - convert highest_perf data type.
> - - modify preferred core init when cpu init and online.
> - acpi: cppc:
> - - modify link of CPPC highest performance.
> - cpufreq:
> - - modify link of CPPC highest performance changed.
> 

This series in now in linux-kselftest next branch for Linux 6.7-rc1.

If there are any changes and/or fixes, please send patches on top of
linux-kselftest next branch.

thanks,
-- Shuah