Power QoS

Introduction

What is QoSPM? Quality of Service power management (QoSPM) allows you to enable aggressive power management for your hardware subsystems, such as your network and CPU, without sacrificing the user's QoS expectations. This project is targeted at the development, application, and enablement of the QoS Power Management (QoSPM) idea.

Why do I care? We want the systems to do the most aggressive power management they can at all times (the more automatic the better), subject to usability and performance constraints.

We expect hardware (mobile devices) to become smarter and more capable of extreme throttling. We expect the hardware to communicate in terms of latencies, throughputs, and timeouts. So, the discussion of this project focuses on these parameters.

How does it work? By providing the QoS expectation information to the subsystems, they can then implement power performance trade-offs that will go unnoticed to the system and user. We feel that it's generally better to have the lower levels of the hardware/software stack implement the power management and, with the communication of QoS expectations to these lower levels, it will be possible to do so.

What are some examples of the benefits? Some QoSPM solutions include:

• improved CPU idle - QoSPM-requested wake up latencies constrain how deep the sleep state of the CPU is allowed to enter when idle (that is, QoSPM-requested operational latencies constrain how deep a C-state to attempt)
• WiFi - QoSPM enables the transmitter power state to be defined by operational latency and bandwidth expectations, such as VoIP, games, and web browsing
• Gigabit Network - network packets and interrupt events can be buffered up to reduce power use at the expense of some latency. If the QoS needs don't call for very low latency, the network driver can automatically set these behaviors.

We welcome community involvement! LessWatts.org will allow a community to help develop the QoSPM infrastructure and solutions. To get involved, join the QoSPM mail list/IRC.