Power management

"We're still pretty stupid about power management," Morton says. Devices are able to support low-power states. For example, a network card that's not receiving incoming traffic can go to a lower-power state. But Linux supports only on and off, and Morton says, "we're having trouble getting off and on working."

Torvalds says that there's a difference between a driver that works -- Linux ships with more than any other OS -- and a driver that implements advanced features of the hardware, such as power-saving modes. Many Linux drivers still lack the latter. "We have a ton of drivers, but 99 percent of all people worry a lot more about basic functionality. Many people would like for the driver to also use power efficiently, and handle suspend/resume well, but it's definitely a secondary concern to 'working'," he says.

Imad Sousou, director of Intel's Open Source Technology Center, says several Intel developers are working on the power problem.

Among the projects is power-saving functionality for multicore processors. On one dual-core processor, putting one core into a low-power "nap" can reduce the processor's power use from 34 to 12 watts, Sousou says. But while power saving for the processor works well in existing Linux installs, much work remains to be done on drivers for PCI devices, he says.

Where Intel controls the hardware and driver, power is a priority, Sousou says. But all the drivers for PCI devices, from a variety of hardware makers and driver authors, need attention in a power-saving project. "You need to do it on a wide spectrum of devices to be effective. We're doing our part," he says.

Unlike big splashy new kernel features, such as new virtualization technologies, the power problem will be a series of little jobs. "I don't think there's anything big that's going to make things better -- it's going to be one thing at a time," Sousou says.

One recent step forward in kernel-side power management is still waiting for other programs to catch up. Development work from Ingo Molnar of Red Hat and Thomas Gleixner, founder of embedded Linux development firm Linutronix, gave Linux a power-conservation feature called "tickless" that shuts down Linux's regular timer interrupt, which typically goes off from 100 to 1,000 times a second. In place of the periodic timer, a tickless kernel wakes up only when needed.

Although tickless holds the potential for putting millions of Linux boxes into cool, power-sipping sleep instead of heat-spewing wakefulness, two limitations hold it back. First, it works only for 32-bit kernels, not the 64-bit ones commonly used on new servers; 64-bit support is said to be coming soon. Second, many user programs still wake up the kernel when they don't have to -- for example, to check for the existence of new files when they could be using functionality called "inotify" to let the kernel tell them when new files appear.

Fedora kernel developer Dave Jones became the spokesman for the trend of power troubleshooting in user space with a talk last year, "Why user space sucks."

This May, the hunt for power-sucking applications got a boost when Intel developer Arjan van de Ven announced the powertop utility. Powertop pinpoints any running programs that, as the project web site puts it, "ruin the party" by waking up the processor.

The One Laptop Per Child project asked for tickless and is in a position to benefit from it quickly, because it's working with a finely tuned set of software. But with powertop available, the information is out there to put the pressure on more of the diverse user applications found on conventional desktop and server boxes to clean up power-hoggish coding.