June 25, 2007 4:00 AM PDT

Linux coders tackle power efficiency

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"If you have a server running 50 virtualized guests, and each guest has a timer tick 1,000 times per second, that is 50 thousand ticks per second, without even doing any work yet," van de Ven said. "With tickless, you go from 1,000 to maybe 10, and suddenly it becomes manageable to do 50 guests."

Michael Larabel, editor of the Phoronix site that tests Linux hardware performance, found the tickless kernel can cut power consumption from 28 watts to 26 watts in IBM's Pentium M-based ThinkPad R52 running Fedora 7.

"A tickless kernel, in conjunction with (processor-based) power-saving technologies, can go a long way in extending the life of the battery and reducing the heat output," Larabel said.

Peeking with PowerTop
A tickless kernel isn't much good if higher-level software requires the kernel to schedule frequent wakeup calls. That's where PowerTop comes in.

"A typical Linux distribution has many components that wake the processor up frequently for no good reason," van de Ven said in an announcement of the software. "PowerTop will provide an indication of which...software components are the biggest offenders in slurping up your battery time."

Scrutiny with PowerTop has uncovered power-draw culprits. The Gvim text editor's blinking cursor wakes up the kernel. Evolution e-mail software needs to check for new jobs to do 10 times a second. The GAIM (now called Pidgin) instant-messaging software checks every 5 seconds to see if it should set itself as "idle."

As well as fixing these sorts of issue, the Linux kernel itself needs to be spruced up to better support its own "ticklessness."

"Even though the kernel itself now has all the fundamental timer-handling knowledge, most of the kernel subsystems use some timers for their own handling, and tuning that usage will probably go on for some time," Torvalds said.

And other frontiers need work, van de Ven said. Device drivers--the software modules that let the kernel communicate with hardware such as network cards or keyboards--need to be revamped to better handle power issues.

Another issue is developing power-related policy management software that governs a computer's behavior based on what its user is doing. And yet another thorny one is supporting laptop suspend-resume abilities better so laptop computers can hibernate gracefully.

"On the suspend/resume side there will be a lot of rearchitecting needed, especially for suspend-to-disk," van de Ven said. "It's an ongoing discussion topic in Linux."

But much of that work can take place on a newly tickless foundation. "The heavy lifting is mostly done," Torvalds said.

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4 comments

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Linux was already well ahead of MS
Like everything else.

Without these changes, my SuSE install on my laptop lasts about 95% longer on batteries then the default XP install.
Posted by qwerty75 (1164 comments )
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Indeed.
Miguel de Icaza and his team of Mono developers just finished a first implementation of Silverlight for Linux (Moonlight) in 21 days:

<a class="jive-link-external" href="http://developers.slashdot.org/developers/07/06/25/1427225.shtml" target="_newWindow">http://developers.slashdot.org/developers/07/06/25/1427225.shtml</a>

Microsoft takes what...a few months to do something that has security holes in it like swiss cheese?

Open Source philosophy will always be ahead of Microsoft due to the open-eyes approach to rapid application development. Applications pop-up, security holes are spotted and patched almost as fast, and nothing can really match it.

The juxtaposition of these two opposing methods simply makes Microsoft look like a second-rate development house of cheap, out-sourced labor. The irony is that OSS is made up of a world of labor that has a fondness for coding, to see things done right and in an open arena.
Posted by `WarpKat (275 comments )
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95%?
SuSE is definately better than XP but I dont know about 95% better unless you have XP set to stay in performance mode.

I did a heavy ammount of tweaking both XP and SuSE when I first got my laptop in early 2004 when the mobile Athlon 64s came out. I'd enabled all kinds of power saving tweaks in XP and the AMD power now features to clock down the CPU while in battery as well as cut graphics performance automatically in bat mode and was able to extend battery life in XP by almost an hr.

Under SuSE though, I redid a tempfs to map to RAM instead of disk so browser cache and various other stuff that writes there would not go to disk, I added in some features to spin down and turn off disks in 5 mins and power down sections of the MB not being used, power down broad cast power on my WiFi if I had a good signal, and clock down the CPU while on battery. I somehow had to turn off that annoying tick message that syslogd writes to logs that kept spinning up the HD also. After all that tweaking and 3 months of work in spare time when I was bored I got about an hr and 30-40 mins extra out of battery from default settings. So about an extra 40-50 mins over XP with all its battery saving features turned on.

Still a huge difference but not 95%

This tickless kernel, however, sounds really cool I'd love to try it out and see what it can do.
Posted by lynxss (39 comments )
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