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AMD P-State is the AMD CPU performance scaling driver that introduces a new CPU frequency control mechanism on AMD Zen based CPU series in Linux kernel. The new mechanism is based on Collaborative processor performance control (CPPC) which is finer grain frequency management than legacy ACPI hardware P-States. Current AMD CPU platforms are using the ACPI P-states driver to manage CPU frequency and clocks with switching only in 3 P-states. AMD P-State is to replace the ACPI P-states controls, allows a flexible, low-latency interface for the Linux kernel to directly communicate the performance hints to hardware. AMD P-State leverages the Linux kernel governors such as *schedutil*, *ondemand*, etc. to manage the performance hints which are provided by CPPC hardware functionality. The first version for AMD P-State is to support one of the Zen3 processors, and we will support more in future after we verify the hardware and SBIOS functionalities. There are two types of hardware implementations for AMD P-State: one is full MSR support and another is shared memory support. It can use X86_FEATURE_CPPC feature flag to distinguish the different types. Using the new AMD P-State method + kernel governors (*schedutil*, *ondemand*, ...) to manage the frequency update is the most appropriate bridge between AMD Zen based hardware processor and Linux kernel, the processor is able to adjust to the most efficiency frequency according to the kernel scheduler loading. Please check the detailed CPU feature and MSR register description in Processor Programming Reference (PPR) for AMD Family 19h Model 51h, Revision A1 Processors: https://www.amd.com/system/files/TechDocs/56569-A1-PUB.zip Signed-off-by: Huang Rui <ray.huang@amd.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.