Documentation/admin-guide/pm/amd-pstate.rst

Source file repositories/reference/linux-study-clean/Documentation/admin-guide/pm/amd-pstate.rst

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System: Linux kernel
Corpus path: Documentation/admin-guide/pm/amd-pstate.rst
Extension: .rst
Size: 52726 bytes
Lines: 869
Domain: Support Tooling And Documentation
Bucket: Documentation
Inferred role: Support Tooling And Documentation: documentation
Status: atlas-only

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.
Defines or uses C structs; map object ownership, embedded links, reference counts, and lock ownership.

Dependency Surface

No C-style include directives detected by the generator.

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No top-level syscall, struct, function, initcall, or export declaration detected by the generator.

Annotated Snippet

.. SPDX-License-Identifier: GPL-2.0
.. include:: <isonum.txt>

===============================================
``amd-pstate`` CPU Performance Scaling Driver
===============================================

:Copyright: |copy| 2021 Advanced Micro Devices, Inc.

:Author: Huang Rui <ray.huang@amd.com>


Introduction
===================

``amd-pstate`` is the AMD CPU performance scaling driver that introduces a
new CPU frequency control mechanism on modern AMD APU and CPU series in
Linux kernel. The new mechanism is based on Collaborative Processor
Performance Control (CPPC) which provides finer grain frequency management
than legacy ACPI hardware P-States. Current AMD CPU/APU platforms are using
the ACPI P-states driver to manage CPU frequency and clocks with switching
only in 3 P-states. CPPC replaces the ACPI P-states controls and allows a
flexible, low-latency interface for the Linux kernel to directly
communicate the performance hints to hardware.

``amd-pstate`` leverages the Linux kernel governors such as ``schedutil``,
``ondemand``, etc. to manage the performance hints which are provided by
CPPC hardware functionality that internally follows the hardware
specification (for details refer to AMD64 Architecture Programmer's Manual
Volume 2: System Programming [1]_). Currently, ``amd-pstate`` supports basic
frequency control function according to kernel governors on some of the
Zen2 and Zen3 processors, and we will implement more AMD specific functions
in future after we verify them on the hardware and SBIOS.


AMD CPPC Overview
=======================

Collaborative Processor Performance Control (CPPC) interface enumerates a
continuous, abstract, and unit-less performance value in a scale that is
not tied to a specific performance state / frequency. This is an ACPI
standard [2]_ which software can specify application performance goals and
hints as a relative target to the infrastructure limits. AMD processors
provide the low latency register model (MSR) instead of an AML code
interpreter for performance adjustments. ``amd-pstate`` will initialize a
``struct cpufreq_driver`` instance, ``amd_pstate_driver``, with the callbacks
to manage each performance update behavior. ::

 Highest Perf ------>+-----------------------+                         +-----------------------+
                     |                       |                         |                       |
                     |                       |                         |                       |
                     |                       |          Max Perf  ---->|                       |
                     |                       |                         |                       |
                     |                       |                         |                       |
 Nominal Perf ------>+-----------------------+                         +-----------------------+
                     |                       |                         |                       |
                     |                       |                         |                       |
                     |                       |                         |                       |
                     |                       |                         |                       |
                     |                       |                         |                       |
                     |                       |                         |                       |
                     |                       |      Desired Perf  ---->|                       |
                     |                       |                         |                       |
                     |                       |                         |                       |
                     |                       |                         |                       |
                     |                       |                         |                       |
                     |                       |                         |                       |
                     |                       |                         |                       |
                     |                       |                         |                       |
                     |                       |                         |                       |

Annotation

Atlas domain: Support Tooling And Documentation / Documentation.
Implementation status: atlas-only.

Implementation Notes

This generated page is the file-by-file coverage layer; curated subsystem chapters should link here when they synthesize a multi-file control flow.
Core OS pages should be promoted from atlas-only to deep-reviewed when they explain data structures, invariants, locking, lifecycle, and C implementation snippets.
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