Introducing the MDP State Driver: Enhancing CPU Performance and Power Efficiency on Linux
Table of Contents
- Introduction
- Background
- Existing Kernel Frequency Control
- The Need for a New CPU Frequency Control Mechanism
- Introducing the MDP State Driver
- Dependency Components for the MDP State Driver
- Functionalities and APIs of the MDP State Driver
- testing and Performance Optimization
- Challenges and Future Improvements
- Conclusion
Introduction
In this article, we will discuss the new CPU frequency control mechanism on Linux known as the MDP State Driver. We will start by providing some background information on the multi-components in the lens kernel, including the CPU, power management, and GPU dim Graphics compute support. Then, we will delve into the existing kernel frequency control mechanisms and the need for a new solution. We will introduce the MDP State Driver and its functionalities and APIs. Next, we will explore the dependency components required for the MDP State Driver to function properly. We will discuss the testing and performance optimization of the driver and highlight the challenges faced and future improvements needed. Finally, we will conclude the article by summarizing the key points discussed.
Background
The MDP State Driver is a new CPU frequency control mechanism introduced in the Linux kernel. It aims to provide a more efficient and optimized solution for managing CPU frequencies and performance on MD processors. The driver is designed to replace the existing ACPI CPU Freak driver, which may not be as performance and power-efficient on modern CPU platforms. The MDP State Driver leverages the CPPC (Collaborative Processor Performance Control) functionality provided by the MD processors and introduces a new kernel module called the MDP State Driver.
Existing Kernel Frequency Control
The existing kernel frequency control mechanisms, such as the ACPI CPU Freak driver and the kernel governors, have been used to control CPU clocks and manage CPU frequencies. However, these mechanisms may not be optimized for MD processors. The ACPI CPU Freak driver, which is based on Intel platforms, may introduce potential issues on MD processors. The MD processors provide a former-based CPU clocks Dynamic Power Management (DPM) solution, but the ACPI CPU Freak driver does not fully utilize this functionality. In contrast, the MDP State Driver utilizes the MSR (Model Specific Register) as the backend mailbox for frequency control, offering lower latency compared to the ACPI AML code interpreter.
The Need for a New CPU Frequency Control Mechanism
The need for a new CPU frequency control mechanism arose due to various reasons. Firstly, the Chrome project required a better performance for rod scaling in their new product, which led to the introduction of the CPPC-based CPU Freak solution. Secondly, while working with engineers to enable Steam Deck on the MD platform, performance issues were identified with the CPU frequency precision and slow motion on certain games. Upon investigation, it was found that the ACPI CPU Freak driver had several problems on MD processors. These issues prompted the exploration and implementation of the MDP State Driver.
Introducing the MDP State Driver
The MDP State Driver is a new kernel module that manages CPU frequency and performance on MD platforms. It leverages the CPPC functionality provided by the MD processors and uses the CPPC frequency range instead of the traditional ACPI 3P states to control CPU frequency. This allows for better optimization using kernel governors, such as the scheduler, to calculate the reasonable design performance values. The driver implements various callbacks and Helper functions to control frequency and performance. It also introduces Trace events and user-space tools for debugging and monitoring the driver's functionalities.
Dependency Components for the MDP State Driver
The MDP State Driver relies on several key components to function properly. Firstly, it interacts with the CPU idle driver in the Linux kernel, which controls the CPU's C0 resistance and sets the CPU from C0 to C1 using the MMWAIT instruction. It also utilizes the kernel governors in the CPU Freak driver, such as the on-demand and performance governors, to manage frequency changes. The MDP State Driver implements the MDP State APIs, which are used by the kernel governors to manage performance Hints for each processor core. It also requires MSR support in the current processor to access the CPPC-related MSR registers.
Functionalities and APIs of the MDP State Driver
The MDP State Driver offers various functionalities and APIs for controlling CPU frequency and performance. It provides callbacks and functions for adjusting performance and frequency, as well as functions for updating the frequency target. The driver further exposes global attributes files in the CRFS to control its functionalities at the system level. These attributes allow users to set the highest, nominal, lowest, and lowest processor performance values and frequencies. Additionally, user-space tools like the CPU Power Tool and the MDP State Tracer Tool provide further control and monitoring capabilities.
Testing and Performance Optimization
To ensure the functionality and performance of the MDP State Driver, testing and performance optimization are crucial. The driver has been tested on multiple CPU benchmarks, such as T-bench and SPEC CPU Bench, to evaluate its performance improvement compared to existing kernel governors. The results show positive improvements in performance, but further optimization is needed, especially in terms of power-based performance. The driver also undergoes continuous testing on existing CPUs to ensure compatibility and functionality. The introduction of unit tests and benchmark automation testing helps in verifying the support of system variants and firmware.
Challenges and Future Improvements
Despite the progress made with the MDP State Driver, there are still challenges to overcome. The driver needs to resolve performance and power issues on various benchmarks to provide consistent improvements. The support for all existing CPUs and platforms, including mobile, desktop, and server, is another area that requires attention. Additionally, optimizing power for gaming on platforms like Steam Deck is a priority. Further improvements in performance and power, as well as customization options for different product requirements, are also part of the future roadmap for the MDP State Driver.
Conclusion
The MDP State Driver introduces a new CPU frequency control mechanism for MD processors in the Linux kernel. It addresses the limitations of the existing ACPI CPU Freak driver and leverages the CPPC functionality to provide better performance and power efficiency. The driver offers various functionalities, APIs, and tools for controlling and monitoring CPU frequency and performance. While it has shown positive improvements in performance, further testing, optimization, and support for different platforms and benchmarks are ongoing efforts. The MDP State Driver has the potential to enhance the performance and power management capabilities of MD processors in a wide range of applications.
Highlights
- The MDP State Driver is a new CPU frequency control mechanism for MD processors.
- It replaces the existing ACPI CPU Freak driver with optimized performance and power efficiency.
- The driver leverages the CPPC functionality and introduces a new kernel module.
- Various functionalities, APIs, and tools are provided for controlling and monitoring CPU frequency.
- Testing, performance optimization, and compatibility with different platforms and benchmarks are ongoing efforts.
- The MDP State Driver has the potential to enhance the performance and power management capabilities of MD processors.
FAQ
Q: What is the MDP State Driver?
A: The MDP State Driver is a new CPU frequency control mechanism designed for MD processors in the Linux kernel.
Q: How does the MDP State Driver improve performance and power efficiency?
A: The driver leverages the CPPC functionality and introduces optimized performance and power management capabilities.
Q: What are the challenges faced by the MDP State Driver?
A: The driver faces challenges in resolving performance and power issues on various benchmarks, supporting all existing CPUs and platforms, and optimizing power for gaming.
Q: What are the future improvements planned for the MDP State Driver?
A: Future improvements include further performance optimizations, customization options, and support for different product requirements.
Q: How can I contribute or get more information about the MDP State Driver?
A: You can reach out to the author directly or access the provided links for more information and documentation.
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