LKML Summary Podcast

Audio: COMING SOON

For Thursday, December 17th, 2009, I’m Jon Masters with a summary of today’s LKML traffic.

In today’s issue: 80 character limits, CFQ group scheduling, DRM, eager NFS writeback, and kbuild.

80 character limits. There has been some discussion of late concerning the historical 80 character limitation imposed upon the length of lines of kernel code, for the benefit of readibility (especially on 80 line VT100 style terminals). As Linus points out, few people use these any more (and most of those are more annoyed by the 24 vertical line limitation). He says he is “driven wild” when strings must be split up and are not easily grepped across lines, and doesn’t feel the 80 character limit is so important any more. He suggests various alternative higher limits.

CFQ group scheduling. Vivek Goyal posted an RFC concerning the structure of CFQ scheduling groups. Specifically, he wants to address the fact that RT tasks are not treated system wide so an RT task within one CFQ cgroup is treated only as having RT priority within that group, but not with respect to other groups that may exist on the system. He listed a variety of proposals involving various hierarchies of task groups that could be implemented to address this issue and asked for some feedback.

DRM. Arnd Bergmann posted a patch entitled “drm: allow unlocked ioctls in drivers”, in which he adds a new flag to ioctls for which he thinks the BKL (Big Kernel Lock) is not required. He “blindly” applied this to “all the most commonly used ioctl commands without checking if they actually rely on the lock”, and was able to reduce BKL use by “90%” on a system. Clearly an RFC patch, but one that is worth some further investigation.

Eager NFS writeback. Steve Rago posted a patch intended to improve the performance of large sequential (client) writes over NFS by implementing eager writeback support. Existing systems utilize a “lazy” writeback approach in which the client will dirty pages faster than they can be written back to the server, and can cause excessive memory pressure for large workloads. Using this patch, and a sysctl called nfs_max_woutstanding, one can now configure how many dirty pages will be allowed before an application will be blocked from dirtying any more until further writes have reached the server. The patch is “almost entirely” based upon a previous patch from Peter Staubach.

Kbuild. The discussion surrounding excessive kernel build dependencies (such as perl, awk, and others also) continued with Peter Anvin weighing in to argue that a dependency on perl might be better than a number of others that would replace it (though he wasn’t endorsing perl as the best posible solution). He also suggested it might be time for the kernel to have its own scripting language, bundled with it, to solve the mess. Rob Landley mentioned that POSIX exists for a reason in implying that the dependency upon non-standard GNU extensions to tools such as awk is worse than a simple dependency upon awk itself. The handling of unicode by tools such as awk also came under discussion.

In today’s announcements: GIT version 1.6.5.7. Junio C Hamano announced the latest version of the GIT SCM is now available on the kernel.org site at http://www.kernel.org/pub/software/scm/git/. The latest version includes a small number of miscellaneous fixes. Junio also announced that the next release candidate for 1.6.6 (rc3) is now available, and this includes a few more updates, but is still a relatively small update.

The latest kernel release was 2.6.32.

Greg Kroah-Hartman posted a number of 2.6.27 stable series kernel review patches (2.6.27.42), a larger number of 2.6.31 stable series review patches (2.6.31.9), and an even larger number of 2.6.32 stable series review patches (2.6.32.2). These were intended to be finalized by the 19th, which has passed as of this podcast being provided.

Stephen Rothwell posted a linux-next tree for December 17th. Since Wednesday, the mips tree inherited conflicts from the mtd tree, the 52xx-and-virtex tree lost its conflict, the kbuild tree inherited a merge fixup from the rr tree, the acpi tree lost its conflicts and build failure, the mtd tree lost its conflicts, the rr tree gained a conflict against Linus’ tree, the voltage tree lost its build failure, the fsnotify tree gained a build failure for which Stephen applied a merge fixup patch, and the hwpoison tree lost its conflicts. The total subtree count remained steady at 155 trees, and Stephen repeated his usual “call for calm” in not merging patches intended for 2.6.34 until after 2.6.33-rc1 has been released.

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

Audio: COMING SOON

For Wednesday, December 16th, 2009, I’m Jon Masters with a summary of today’s LKML traffic.

In today’s issue: Devtmpfs, kernel.h, mm, and power management.

Devtmpfs. Al Viro came forth with a couple of remarks concerning devtmpfs. He feels that there is a race waiting to happen with the code using a kstrdup (that might sleep) while holding an rwlock. This situation could arise in the case that a call is made to device_add, for example. Separately, Al posted part one of his VFS updates for the 2.6.33 kernel.

Kernel.h. Joe Perches posted a number of cleanups against the kernel.h header file, which he described as a “chaotic jumble collected over time”. Since, apparently, nobody specifically owns this, he sent the patches to Linus.

MM. Hiroyuki Kamezawa posted an updated eleven part patch series based upon Christoph Lameter’s mm_accessor patch that had been posted on November 5th. These patches replace all accesses to mm->mmap_sem with accessor functions that can be used to optimize such accesses in the future, for example by not taking mmap_sem in certain situations. Hiroyuki believes that the patch size is very large and so for eventual merging, it will be necessary to implement it in stages, with architectures later.

Power Management. Ingo Molnar sent his usual round of updates for the 2.6.33 merge window, including some updated Power Management patches. These contain, amongst other things, a patch from Arjan van de Ven that can be used to chart suspend and resume times for devices (especially when doing async suspend and resume, but also otherwise). Arjan continues to facilitate charting of boot and other latencies in getting devices up and running under Linux. On the subject of asynchronous suspend and resume, Linus Torvalds weighed in with some comments on the relative difficulty of asynchronous suspend and resume as applied to Cardbus bridges with many attached devices.

In today’s announcements: LTTng 0.182. Mathieu Desnoyers announced the release of LTTng 0.182 for the 2.6.32 series kernel. The latest release fixes builds on ppc440, and adds full support for ARM omap3 to the trace clock code (power management support, DVFS). Separately, Mathieu announced LTTV 0.12.25, the corresponding view tool that includes support for reading traces taken from an ARM omap3-based board.

The latest kernel release was 2.6.32.

Stephen Rothwell posted a linux-next tree for December 16th. Since Tuesday, the origin tree lost its build failure, the avr32 tree lost its conflict, the microblaze tree lost its conflict, the mips tree lost 4 of its conflicts, the acpi tree still had a build failure so the version from Friday was used (it also gianed a conflict against Linus’ tree), the hwpoison tree gained a conflict against Linus’ tree and also a build failure for which Stephen applied a merge fixup patch. The total subtree count remained steady at 155 trees and Stephen repeated his usual “call for calm” in not merging patches intended for 2.6.34 until after 2.6.33-rc1 has been released.

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