September 2013 Linux Kernel News

Mainline Release (Linus's tree) News

Linus Torvalds closed the 3.12 merge window when he released 3.12-rc1. tty layer and scalability improvements received a special mention in the release announcement. The tty layer cleanups lead to per-tty locking which will result in better performance on some work-loads.

The directory entry (dentry) object represents a component in the filename path. For example, in the path /usr/bin/yelp, each individual component in the path, /,usr,/,bin,/,yelp are all dentry objects. Using dentry objects helps make the process of validating and resolving each competent in the path easier. With the dentry reference or usage count scalability work that is included in 3.12-rc1, the filename caches now scale very well in 3.12. This work eliminates the per-dentry lock contention even on the same file or directory lookups.

Please read the 3.12-rc1 release announcement for a list of what else is in this release.

3.12-rc2 release came out one week later on September 23. This release contains a few driver bug fixes and 24 AMD Radeon driver patches from Alex Duecher. In addition to several bug fix patches, dynamic power management enablement for current and upcoming AMD processors Trinity, Kaveri, and Kabini is in this rc release. Please read the 3.12-rc2 release announcement for complete release notes.

3.12-rc3 is released on September 29 2013. This rc has seen some churn in mm area with reverting a few commits that were still being discussed, and allow the discussion to be completed and patches revised as needed. Bulk of the changes are in the driver space and new lockref support for ARM and s390. Please read the 3.12-rc3 release announcement for complete release notes.

Stable release News

As of this writing the latest stable releases are as follows:

  • Stable 3.11: Current latest version is 3.11.3
  • Longterm 3.10: Current latest version is 3.10.14. Projected EOL is September 2015.
  • Longterm 3.4: Current latest version is 3.4.64. Projected EOL is October 2014.
  • Longterm 3.2: Current latest version is 3.2.51. Projected EOL is 2016.
  • Longterm 3.0: Current latest version is 3.0.98. Projected EOL is October 2013.
  • Extended stable 3.8.y.z: Current latest version is
  • Extended stable 3.5.y.z: Current latest version is
  • Longterm 2.6.34: Current latest version is Projected EOL is mid-2013
  • Longterm 2.6.32: Current latest version is Projected EOL is mid-2014
  • Linux RT stable releases are numerous. Please checkout linux-stable-rt.git for their latest versions.

If you ever wondered how these stable releases are managed and how often a new release comes out, here is more detail: Active kernel releases

Where can you find all git trees for Linux releases?

  • Mainline: git://
  • Stable releases (current and longterm): git://
  • Linux RT releases: git://
  • Extended stable releases: git://
  • Bleeding edge linux-next: git://

Cloning into git tree and build new kernel

It is very easy to clone into one of these gits and build your own kernel. For example, run the following command to clone into stable git. It will create a new stable_git directory and clone into the linux-stable.git. You will find the Linux sources in the newly created stable_git directory. Once the git is ready, run make commands as shown below.

  1. Cloning into stable git

    $ git clone git:// stable_git
  2. Now how do you build a new kernel using oldconfig from your stock kernel?

    $ make oldconfig
    $ make all 

LinuxCon North America and co-located events News

LinuxCon North America was held from September 16-18, 2013 in New Orleans, LA. Linux Conferences provide opportunities to developers to come together to discuss new ideas and solutions to problems in face to face meetings. In addition to face to face developer meetings, Linux Conferences also feature talks and presentations on various Linux Kernel and Linux Kernel eco-system topics by Linux developers and Open Source experts. Read on for my thoughts and take away from the LinuxCon NA and sessions I attended.

Keynote Panel: Linux Kernel Developer Panel - Tejun Heo, Red Hat; Greg Kroah-Hartman, Linux Foundation; Sarah Sharp, Intel; Linus Torvalds, Linux Foundation; Moderated By Ric Wheeler, Red Hat

Please visit the event home page linuxcon-north-america_2013 for comments and insights from this panel discussion. I found this panel discussion informative. It helps new kernel developers and companies new to contributing to Linux kernel understand how the maintainers think, and what would help them do their job effectively. My take away and comments that resonated with me are:

"It's essential to budget extra time and resources to get patches upstream." - Tejun Heo
"Not just be really early, but be really involved. If you build your patch within the walls of your company, the thing solves your problem but nobody else's problem. In order to get things merged you need to solve not just your problem, but realize the kernel is bigger than your company." - Linus Torvalds
"I was always into computers, and I wanted to work with operating systems. I'm from Korea and I didn't know how I would get a job with MS or Sun and I didn't speak English. But with Linux it didn't matter where I came from or degree I had, if you can do it, you can do it. It doesn't matter who you are are where you came from." - Tejun Heo
UEFI and Linux - Kirk Bresniker, HP

This talk goes over the history of EFI and ACPI, UEFI standards, and what is happening in this area. This is an area I keep an eye on to be aware of the progress and work that is happening. One interesting piece of information that I learned in this talk is the desire to build 32-bit x86 systems with UEFI support. This is interesting for the UEFI standard and implementation. The fact that UEFI executes in native mode and 32-bit UEFI systems can't execute 64-bit firmware makes it challenging to support operating systems on these systems. In addition, 64-bit OS won't boot on 32-bit UEFI systems. Further more, it is not a trivial effort to add UEFI 32-bit support to Linux kernel. So, it is better to stay away from supporting UEFI on 32-bit systems and stick with BIOS. For more information on 32-bit UEFI systems, please read Matthew Garrett's article Don't ship 32-bit UEFI firmware on x86

Linux Plumbers Conference 2013 ACPI/PM PCI Subsystems Micro-conference

Various ACPI/PM PCI sub-system technical issues and topics were discussed at this all-day event. The ACPI vs Device Tree discussion was by far the most productive and important at this conference. This discussion was on how to add Linux kernel support for new ARM systems that describe devices using these two enumeration methods. Some very concrete action items came out of this fast moving and spirited discussion between the Device Tree and ACPI experts, Grant Likely (Linaro), Mathew Garrett (Nebula), Rafael Wysocki (Intel, ACPI, and Linux PM maintainer), H. Peter Anvin, and David Woodhouse. In essence, device drivers should not have to know the details of Device Tree, and there should be a glue layer API for drivers to call to fetch the device information that is described in underlying Device Tree or ACPI layer.

You can read all about the discussion on this topic and other topics at: lpc2013-acpipm-pci-subsystems

Final Thoughts

Next up is the 3.12-rc3 release and a few more 3.12-rcs prior to releasing 3.12. LinuxCon NA and other Linux conferences are important cogs in the Linux ecosystem which bring Linux kernel developers and industry members together and help move Linux forward. As a Linux kernel developer, for me, these events are the opportunities to meet co-developers and discuss issues, problems, and learn, or just catchup, without which developers are just names and email addresses. Next up is the Linux Kernel Summit, LinuxCon EU, and co-located events scheduled to be held in Edinburgh, UK from October 21-25, 2013. I am looking forward to presenting and attending.

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