Linux systems' power consumption is rapidly becoming a top concern for operators of large datacentres.
A University of California study recently attributed 90% of the increase in datacentre 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 representing 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 1,000th 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 datacentre. 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 behaviour 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 enters a room and then leaves them on when he departs a minute later. PowerTOP points the finger at programs that wake up the system.