Devtmpfs, aka 'devfs 2.0' to its detractors, should allow the Linux kernel to start faster and run without udev. Support has been added for ACPI 4.0 and there are two new make targets which generate kernel configurations attuned to the running system. Changes to the power management subsystem increase data throughput and allow better use of runtime power saving features on modern I/O devices.

Last week we reported that the open-source ATI Linux driver had picked up improved power management in the form of dynamic power management and power management profiles that can be defined by the end-user.

"...Recently I bought an Eee 901. Asus has modified the kernel's ACPI driver. They released the source code to that on an 8G surf model, but the 901 has additional hardware features in the ACPI space (bluetooth radio power toggle, for instance) that are not in the source they released back then. There are no sources released at all under the 901 section of their website.

In part 1 of this series we learned how to measure how much power our systems are using, both hardware and software, and some tricks for reducing power usage without degrading performance. Today we're going to dive into the world of power management on laptops: ACPI, APM, hard disk spindowns, and spinups.

The Open Source Technology Center (OSTC) at Intel has launched a Web site, LessWatts.org, to help Linux users maximize power savings. The site hosts several open source projects, and shares tips and tricks to help optimize power consumption on hardware from portable devices running on batteries to large data centers.

"Major Linux distributors have been shipping ACPI in Linux for several years, yet mis-perceptions about ACPI persist in the Linux community. This paper addresses the most common myths about ACPI in Linux [.pdf]."

Less than a week after Linux kernel 2.6.31 was released, the kernel developers are beginning to submit changes and improvements across virtualization, power management, file systems and device driver code for the upcoming 2.6.32 version.

Red Hat's Matthew Garrett has actively been working on improving power management with graphics processors via the various open-source X.Org drivers. There is quite a lot of work involved, but at the FOSDEM X.Org meeting he shared an update on his progress. In particular, Matthew is trying to conserve power with the GPU, memory, outputs, and displays.

As the kernel and user space exist in different virtual address spaces, there are special considerations for moving data between them. Explore the ideas behind virtual address spaces and the kernel APIs for data movement to and from user space, and learn some of the other mapping techniques used to map memory.