LKML Summary Podcast

Audio: http://media.libsyn.com/media/jcm/linux_kernel_podcast_20100228.mp3

For the weekend of February 28th 2010, I’m Jon Masters with a summary of the week’s LKML traffic.

In today’s issue: Linux 2.6.33, ACPI, Cgroups, Checkpoint and Restart, OF Device Tree, Firmware, and x86 embedded.

Linux 2.6.33. Linus Torvalds announced the final release of 2.6.33 on Wednesday February 24th at 12:06pm Best Coast Time (PST). The final release includes a relatively small number of final fixes on top of rc8. As Linus says, the most notable thing may be the Nouveau integration and modesetting support. Others may notice the mainlining of DRBD and the fact that the AS IO scheduler is now gone (”since keeping it around and just causing confusion seemed to not be worth it any more. You’re supposed to use CFQ instead”). Daniel walker asked Linus whether he still planned to try a one week merge window this time, to which Linus said, “No. But I might do a ten-to-twelve day thing or something like that – just to make sure that anybody who tries to game the system and send their merge request late will get summarily ignored. So I’m going to stop being so predictable that people can tell that exactly two weeks after the last release is where the merge window closes, and if people want to make sure their stuff merged, I had better have a merge request in my inbox earlier than thirteen days after the release.” The pull requests started pretty much immediately, and with the usual vigor. Separately, Con Kolivas announced 2.6.33-ck1, which includes his BFS scheduler and various other “desktop” focused bits.

ACPI. Rafael J. Wysocki posted an RFC patch concerned with removing race conditions from ACPI event handlers. The first race concerns the execution of handlers while they are being removed, the second is a locking issue.

Cgroups. Andrea Righi posted an intruiging RFC patch series intended to provide per-cgroup dirty page limits. The idea is that the maximum amount of dirty pages a cgroup is allowed to have can be limited, and if a cgroup exceeds this count, it will be forced to perform write-out immediately.

Checkpoint and restart. Oren Laaden posted version 19 of his “Linux Checkpoint-Restart” patchset. As a reminder, these patches are intended to allow systems to handle failures by taking whole system checkpoints and restarting all activity from that point in the event of failure. The latest patchset is intended to address previous concerns from Andrew Morton and others, and is apparently able to checkpoint and restart both screen and vnc sessions, and support live migration of network servers between hosts. The project has a checklist of TODOs on its wiki: http://ckpt.wiki.kernel.org/.

OF Device Tree. Grant Likely asked Linus to pull in his OF device tree rework for 2.6.34. Grant has recently been working on ARM support, in addition to the PowerPC, Microblaze, and SPARC changes covered in this pull. Hopefully, OF device tree emulation will finally provide one mechanism for supplying data to the kernel that can be common across many different architectures, in addition to those that do “real” OpenFirmware in the vendor firmware.

Firmware. There was some discussion about kernel firmware versioning, and whether kernel firmware should be wrapped in a container format making it more suited to SO library style versioning. This happened in response to the folks behind the open sourcing of the Atheros WiFi firmware seeking advice on the best way to handle compatible and incompatible versions. David Woodhouse has advocated for the use of more library-like versioning, but was not a big fan of introducing the complexity of such wrappers. In the end it was decided that the kernel developer maintained linux-firmware package should provide firmware files of the form foo-$(API). Those wanting a sub-versioned file like foo-$(API)-$(VAR) could provide one if they so wish.

x86 embedded. Graeme Russ posted a very detailed and well reasoned description of his embedded x86 port, which is not in any way based upon PC hardware, in which he uses U-Boot to transition to 32-bit Protected Mode and directly calls the kernel’s “32-bit BOOT PROTOCOL” described in Documentation/x86/boot.txt. He was having some issues though handling kernel relocation that turned out to be due to documentation differences between the bzImage format and the current reality. Peter Anvin was his usually very helpful self.

In today’s miscellaneous items: A fix for SPARC32 from Rob Landley (apparently, SPARC32 has been broken since 2.6.28, which isn’t surprising since this author and most other Linux SPARC users seem to be running SPARC64 kernels), various debugging from Thomas Gleixner and John Kacur on the recent 2.6.33 RT patch, version 6 of a patch series intended to add lockdep-based diagnostics to rcu_dereference() from Paul McKenney, a series of PPS implementation patches from Rodolfo Giometti (useful for those needing accurate time sources on a serial line), a patch to increase readahead size to a default of 512K from Fengguang Wu (the previous default was 128K), a bunch of s390 updates for 2.6.33 final from Martin Schwidefsky (including kernel image compression “finally…after only 10 years”), some patches intended to document the rfkill sysfs ABI from Florian Mickler, some more nested SVM (virtualization within virtualization on AMD compatible systems) from Joerg Roedel intended to aid running Microsoft Hyper-V with nested SVM (which doesn’t quite work yet even with these according to Joerg), a number of rather cool gdb and early debug updates from Jason Wessel (who has now split kdb and early debug out into two separate trees), version 4 of the “concurrency managed workqueue” from Tejun Heo, a discussion about order 1 allocation failures started by Frans Pop (the failures were under GFP_ATOMIC, but Frans felt that they were particularly ugly given plenty of cache was available for reclaim), David Howells proposed removing EXPERIMENTAL from NFS_FSCACHE in order that it could be compiled into the standard Ubuntu kernel (since, as he says, “As Arjan van de Ven pointed out…the EXPERIMENTAL flag doesn’t mean that much any more”, and a lengthy discussion of linux-next “requirements” that is worth reading, if you have the time.

In today’s announcements:

iproute2. Stephen Hemminger announced release 2.6.33 of the iproute2 utilities that “includes bug fixes and support for all the new features in kernel 2.6.33. This integrates a number of minor bug fixes from Debian aswell”. The update is available at http://devresources.linux-foundation.org/.

RT 2.6.33-rt4. Thomas Gleixner announced version 2.6.33-rt{2,3,4} of the RT kernel patchset. This updates to Linus’ latest tree and includes a number of fixes to bugs reported by John Kacur and others. It is available from the usual location: http://www.kernel.org/pub/linux/kernel/projects/rt/ Thomas noted that “rt/2.6.33 branch is now stabilization only. The rt/head branch will follow linus tree from now on, so it will inherit all (mis)features which come in the merge window. Separately, John Stultz announced that he had forward ported Nick Piggin’s VFS scalability patches to 2.6.33-rc8-rt2, and that it applies to 2.6.33 without any collisions. He requested feedback as he had yet to do any serious stress testing with the patchset (yet).

The latest kernel release was 2.6.33.

Greg Kroah-Hartman released an updated stable Linux 2.6.32.9.

Finally today, Mikael Abrahamsson suggested that some TLC be given to the Wikipedia article on the Linux kernel as it “doesn’t even mention the new -rc system” (in the “development model” section of the article). He wondered if anyone who knew exactly what was going on could write up the new world order on that wiki page for the rest of the world to see. That does not seem to have happened as of this writing.

That’s a summary of today’s Linux Kernel Mailing List traffic, for further information visit www.kernel.org. I’m Jon Masters.