LKML Summary Podcast

Audio: http://media.libsyn.com/media/jcm/linux_kernel_podcast_20091112.mp3

[NOTE] Last week was another 100+ hour week of vendor kernel excitement, and so the podcast suffered as a result. I’m catching up over the US Thanksgiving Day holiday, so expect us to be caught up by the end of November, or thereabouts.

For Thursday, November 12th, 2009, I’m Jon Masters with a summary of today’s LKML traffic.

In today’s issue: Breaking strings, cputime, ftrace, KVM, and XFS.

Breaking strings. Ingo Molnar (in replying to a percpu fixes for 2.6.32-rc6 thread) brought up the issue of breaking strings mid-sentence. He favors re-engineering code such that strings are – in general – on a single source line and more easily greppable (using ‘git grep’, for example). Tejun saw Ingo’s point, but suggested that a more scalable and longer term fix would be to teach grepping tools to understand strings split in such a fashion. This lead onto the comment of the day for today, from Oliver Neukum: “There’s a point where following style guidelines turns into a fetish”. Dear goodness.

cputime. Hidetoshi Seto noted that a recent commit to task_s and utime changed their return types to (the more fine-grained) cputime_t, but without making some other appropriate changes to casts of the return value elsewhere, which affected the granularity of the results of such uses. He posted a patch.

Ftrace. Steven Rostedt has been busy profiling his ftrace infrastructure, looking for issues in the recording of individual entries into the per-cpu managed ring_buffer implementation. He has found that the timestamping feature causes the highest single overhead component in profile runs and is working on moving some of the timestamp processing to the read side of traces.

KVM. The previous discussion on quirks for the AMD Geode CPU (causing it to become viewed as an i686-like processor) had turned into a discussion of hypervisor technology [this happens often], and in particular a bug that Willy Tarreau and others have recently discovered in KVM’s instruction interpreter. It turns out that feeding it arbitrarily long instructions with many “66″ (data size prefix) codes pre-pended will cause KVM to deprive other tasks form running and can be a form of denial of service. Of course, more modern ISAs use fixed width instructions and don’t suffer from these problems, but that isn’t a reason not to address the issue when handling the venerable x86.

XFS. Christoph Hellwig posted an “XFS status update for October 2009″, in which he mentioned that the 2.6.32 merge window had opened up with a major XFS update that included refactoring the inode allocator (performance, etc.), and also noted that a healthy amount of work has recently gone into xfsprogs.

In today’s announcements: Linux 2.6.32-rc7. Linus Torvalds announced the latest release of the 2.6 series kernel at 4:57pm Best Coast Time (PST). In his announcement, Linus notes that he had held off releasing the -rc while Rafael J. Wysocki tracked down an “ugly-looking” resume regression. The changes were otherwise fairly minimal and in line with this stage in rc.

The latest kernel release was 2.6.32-rc7.

Stephen Rothwell posted a linux-next tree for November 12th. Since Wednesday, there were issues with Linus’ tree, the cpufreq, i7core_edac, and sysctl trees, while the net, tip, and usb trees lost conflicts. Rusty’s “rr” tree lost a build failure but exposed problems with the powerpc and sparc trees. The total number of sub-trees now stands at 148 in the latest compose.

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