Speedy 'Wonder Patch' Debuts in New Linux Kernel

Back in November I wrote about the 233-line patch that was expected to bring a huge speed boost to version 2.6.38 of the Linux kernel, and that's just what made its widely anticipated debut on Monday night.

Linux creator Linus Torvalds gave Linux 2.6.38 its official sendoff after just 10 weeks or so of development, noting that it brought several significant changes since the release of version 2.6.37 earlier this year.

"As to the 'big picture,' ie all the changes since 2.6.37, my personal favorite remains the VFS name lookup changes," Torvalds wrote, referring to tweaks made to Linux's Virtual File System (VFS), which acts as a buffer between applications and file systems. "On the whole I think it was surprisingly smooth."

'Some Seriously Good Stuff'

Specifically, VFS now taps the RCU (Read-Copy-Update) path name lookup mechanism to speed performance considerably in some cases.

"It's some seriously good stuff, and gets rid of the last main global lock that really tends to hurt some kernel loads," Torvalds explained in an email in January.

"What's really nice about it is that it actually improves performance a lot even for single-threaded loads (on an SMP kernel), because it gets rid of some of the most expensive parts of path component lookup, which was the d_lock on every component lookup," he added. "So I'm seeing improvements of 30-50% on some seriously pathname-lookup intensive loads."

'It Can Be Very Noticeable'

Torvalds' other favorite addition--and the one commonly referred to now as the 233-line "wonder patch"--is the use of group scheduling to improve desktop interactivity under heavy loads.

"It really works very well for the kinds of things it is designed for," Torvalds wrote. "If you still do 'real work' in a terminal window, you're likely to appreciate it. Compile in parallel in one window, watch a movie in another, and the movie is really smooth. It can be very noticeable indeed."

Early tests found that the patch decreased the average latency of the desktop by about 60 times, as I noted last fall. Two videos on Phoronix demonstrate the difference.

'A Metric Ton of Other Features'

Rounding out version 2.6.38 of the kernel are "a metric ton of other features," as Torvalds put it, noting that drivers account for about half of the changes.

Indeed, both graphics and Wi-Fi are reportedly improved through better support for chips by AMD, Nvidia and Intel along with Atheros, Broadcom and Realtek, for example. More details can be found on the Linux Kernel Newbies Web site.

For users, Linux 2.6.38 is one more thing to look forward to in distributions including Ubuntu 11.04 and Fedora 15, both due this spring. What was that critics were saying about Linux being dead on the desktop?

Follow Katherine Noyes on Twitter: @Noyesk.

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