David Flynn20 September 2007, 10:57 PM
IDF San Francisco |Intel makes further inroads by working with the open-source community, including Canonical and Red Hat, to boost battery life on laptops running Linux.
How times change. A few short years ago the only OS on show at Intel's San Francisco developer forums was Windows, and the only place you'd see a Mac was two blocks away at the Apple store. Now Microsoft has been shuffled aside from the IDF stage to make room Mac notebooks and desktops and, perhaps more worrying to Redmond, Linux. Intel's ultra-mobile platform leans heavily towards Linux, with executives from RedHat and Cannonical appearing during keynotes at the last two IDFs.
Today Intel went a step further, launching an initiative named LessWatts.org which aims to reduce the power consumption of Linux systems from servers to notebooks and ultra-mobile devices. The company has already demonstrated that power-optimised versions of software, which Intel developers have been working on and feeding back into the open source community, can boost the battery life of a Linux laptop by almost a third and add a full hour to its uptime when away from an AC outlet.
"One app can break the entire power savings of a laptop, and that's true for Windows and Linux" says Arjan Van de ven, who leads Intel's Linux software engineering team for making Penguin-friendly CPUs and chipsets.
"Our CPUs like to be asleep for between 10-15ms at a time to get maximum power saving, so if an app wakes up every millisecond you completely ruin the power saving. What we've done, and not just Intel but the Linux community as a whole, is that Linux went to a tickless idle model. The kernel used to do a timing tick every 4ms or 1ms to check if there was work to be done. So every 4ms you take the CPU out of sleep, see if there was work to be done, then send it back to sleep, and the transition alone was really expensive in terms of power. In tickless idle, we check when the next work item is due and then tell the kernel to wake up at that point."
But only limited savings by moving the kernel to this ‘wake on demand' model "are only half the story", Van de ven told apcmag.com. "When we started we thought ‘we'll do the kernel and then we'll be done'. But we also had to fix applications so that they don't keep the CPU busy when they're not doing anything, otherwise they're keeping the CPU awake when it should be asleep."
Intel created a utility named PowerTop to reveal the applications that were most guilty of waking the CPU, "and we started going through those, working down from the top of that list" explains Van de ven, who listed Firefox, Evolution and ‘a lot of Gnome infrastructure' as prime offenders.
The effort appears to have been worthwhile. Van de ven demonstrated two ThinkPad T61 ‘Santa Rosa' notebooks, identical but for the kernel and applications. The notebook running a power-optimised environment was drawing 15.6 watts compared to the 23.3 watt drain of the standard install. Given the T61's 56 watt/hour battery, those figures equate to a respective battery life of 3.5 hours and 2.4 hours - a clear hour's gain.
"Half of our the patches are in the community already, and the other half are being submitted for the next kernel version 2.6.24" says Van de ven. "We've worked with developers on Ubuntu and Fedora and I expect their next versions to have these, or at least most of these for their October releases".
David Flynn is attending IDF San Francisco 2007 as a guest of Intel Australia