22 November 2011, 15:00

Kernel Log: real-time kernel goes Linux 3.0

by Thorsten Leemhuis

The patches for real-time support are now based on a much more recent kernel version. Torvalds has revoked a change merged into 3.2 which had come under widespread criticism from developers. AMD and Intel have released new graphics drivers.

With the release of real-time (RT) kernel 3.0.9-rt25, Thomas Gleixner has declared that the Linux 3.0-based RT tree is now ready for use in live systems. He noted that this new version series represents a major leap forward and that development has run pretty smoothly, despite major revisions to many of the core techniques.

Gleixner has now handed over responsibility for maintaining RT patches for Linux 3.0 to Steven Rostedt, who recently released a pre-release version of Linux 3.0.9-rt26 for evaluation. Gleixner has ported the changes aimed at improving real-time properties to pre-release versions of Linux 3.2 (1, 2, 3). The RT patch has shrunk substantially in the process, as some of the changes have now been incorporated into the main development tree.

Kernel version status

In view of the maturity of the RT patch for Linux 3.0, Greg Kroah-Hartman is ending support for the 2.6.33 series with the release of Linux 2.6.33.20. As of late it had been being maintained solely for the benefit of real-time developers, with the previous stable real-time patch based on Linux 2.6.33.

Kroah-Hartman has also released stable versions 2.6.32.48, 3.0.9 and 3.1.1. The two 3.x stable versions each include more than 200 minor enhancements and bug fixes. The 3.0.10 and 3.1.2 kernels have just been released too. Most stable and long term kernels are now available from a git repository on Kernel.org.

As predicted in the first Kernel Log in the "Coming in 3.2" series, last week Linus Torvalds released the second pre-release version of Linux 3.2, with the third set to follow shortly. The latter will see the removal of a system for user-friendly disk names, merged during the 3.2 merge window, which has since come in for flak from a number of key kernel hackers. The developer behind the patch now plans to implement a userspace solution to achieve the same objective.

RC3 includes a number of patches produced using information gleaned from Windows drivers which deactivate power saving feature ASPM (Active State Power Management) with specific hardware configurations. The patch to restore the PCIe power-saving technology to being active by default on many systems is not, however, set to make its way into the kernel until Linux 3.3. Fedora and Ubuntu have nonetheless already integrated this change into some of their kernels for testing purposes.

In brief

Kernel

Luis R. Rodriguez has announced new versions of compat-wireless, which allow the Wi-Fi drivers designed for Linux 3.2 to be used with older kernel versions.

In a recent email, Andrew Morton mentioned in passing that he is now sending changes he has collected to Stephen Rothwell on an irregular basis for inclusion in linux-next. He notes that this renders the mmotm (mm-of-the-moment) kernel tree, which he has until now been maintaining, largely obsolete, and suggests that users should instead just test linux-next.

Joel Becker, who maintains cluster file system OCFS2, has cleared up a misconception by noting that OCFS2 developers have not been updating the file system version number recorded in the kernel, according to which the version number for OCFS2 in the main Linux development tree is currently stuck at version 1.5. Code in 1.6.x versions of OCFS2 is based on code from the main development tree.

Fedora 15 users are receiving updates containing kernel 3.1 redesignated as 2.6.41; they have previously been served version 3.0 as 2.6.40. This is to avoid problems with applications which are unable to deal with the new version number.

Videos of some of the presentations at LinuxCon Europe 2011 and Embedded Linux Conference Europe 2011 (held at the same time and place and discussed in the last regular Kernel Log) are available on Free Electrons, a web site aimed primarily at embedded Linux developers. The videos include a 'kernel panel' discussion featuring Linus Torvalds, Alan Cox, Thomas Gleixner and Paul McKenney. A video of Gleixner's presentation, in which he provides background information on the state of development of the real-time patch for Linux, is also available.