Power management has been one of the focus points for improvements for Fedora 20. This document provides guidance and information regarding power management for systems running Fedora 20.
1.1. Importance of Power Management
Power management is about studying the different tasks your system performs and configuring each component to effectively optimize its energy consumption while keeping its performance. Correct use of power management results in:
reduced overall energy consumption and reduced electricity costs
reduced heat for servers and computing centers
reduced secondary costs, including cooling, space, cables, generators, and uninterruptible power supplies (UPS)
extended battery life for laptops
lower carbon dioxide output
meeting government regulations or legal requirements such as
Energy Star
meeting company guidelines for new systems
Lowering the power consumption of your whole system or of a specific component leads to lowering their performance. As such, you should thoroughly study and test the decrease in performance you can afford for your configurations, especially on mission-critical systems.
By studying the different tasks that your system performs, and configuring each component to ensure its performance is sufficient for the job, you can save energy, generate less heat, and optimize battery life for laptops. Many of the principles for analysis and tuning of a system in regard to power consumption are similar to those for performance tuning. To some degree, power management and performance tuning are opposite approaches to system configuration, because systems are usually optimized either towards performance or power consumption. This guide describes the tools and techniques that the Fedora Project provides for lowering power consumption.
A lot of new power management features have been introduced to Fedora 20 that are enabled by default. They are all selectively chosen to not impact the performance of a typical server or desktop use case. However, for very specific use cases where maximum throughput, lowest latency, or highest CPU performance is absolutely required, a review of those defaults might be necessary.
To decide whether you should optimize your machines using the techniques described in this document, consider the following questions:
- Must I optimize?
The importance of power optimization depends on whether your company has guidelines that need to be followed or if there are any regulations that you have to fulfill.
- How much do I need to optimize?
Several of the techniques present in this guide do not require you to go through the whole process of auditing and analyzing your machine in detail but instead offer a set of general optimizations that typically improve power usage. Those will typically not be as good as a manually audited and optimized system, but provide a good compromise.
- Will optimization reduce system performance to an unacceptable level?
Most of the techniques described in this document impact the performance of your system noticeably. If you choose to implement power management beyond the defaults already in place in Fedora 20, you should monitor the performance of the system after power optimization and decide if the performance loss is acceptable.
- Will the time and resources spent to optimize the system outweigh the gains achieved?
Optimizing a single system manually, following the whole process is typically not worth it as the time and cost spent doing so is far higher than the typical benefit you would get over the lifetime of a single machine. On the other hand, if you are deploying 10000 desktop systems to your offices all using the same configuration and setup, then creating one optimized setup and applying that to all 10000 machines is a good idea.
