Linux tool points out power-wasting applications

This year's most important Linux application may be a simple utility that helps users spot long-standing bugs that make systems waste power.

By Don Marti, LinuxWorld.com, 07/27/07

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Linux systems' power consumption is rapidly becoming a top concern for operators of large data centers. A University of California Berkeley study recently attributed 90% of the increase in data center power consumption to servers priced at less than $25,000 each, the market where Linux is most important.

But until recently, kernel developers have focused mostly on correctness and performance, leaving the hardware's power-saving features largely unused.

This year, the trend is finally turning around. Problems that get measured get fixed, and an alliance of developers across many different projects is coming together around a modest-looking text-based tool called PowerTOP. PowerTOP's author is Arjan van de Ven, a Linux developer working at Intel.

Thanks to new functionality called "tickless", Linux systems can go into low-power states, and stay there, without having to handle an internal timer every 100th to 1000th of a second. But the catch is that any program that does unnecessary work will wake up the whole machine, giving up the power savings.

PowerTOP's documentation explains, "Current processors save a lot of power if they are idle for long periods, which translates into a longer battery life for your laptop, or a lower energy bill for your data center. However, a Linux system consists of more software than just the kernel, and there are many tunables involved. It's not easy to see what is going on, and as a result the behavior is sometimes far from optimal, and a lot of power is wasted."

In other words, some of the software on a Linux system is like the person who turns the lights on when he comes in the room, then leaves them on when leaving a minute later. PowerTOP points the finger at programs that wake up the system.

When van de Ven first announced PowerTOP this May, Intel launched a companion Web site featuring some power-saving measures that the tool uncovered. A few have been simple tweaks, such as switching from blinking to non-blinking cursors, but most are just examples of power-insensitive coding.

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