LKML Summary Podcast

Audio: http://media.libsyn.com/media/jcm/linux_kernel_podcast_20090629.mp3

For Monday, June 29th 2009, I’m Jon Masters with a summary of today’s LKML traffic.

In today’s issue: Boot consoles, HTC Dream, KSM, and Performance Counters.

Boot Consoles. Robin Getz (of the Blackfin project) posted an RFC allowing more than one “boot console”. Boot consoles are intended for early in boot, and rely upon an additional parameter of CON_BOOT passed to register_console. Existing Linux systems allow only one boot console at a time – the first time a call to register_console is performed without CON_BOOT, any boot console is silently unregistered. Robin’s patch allows multiple boot consoles.

HTC. The HTC Dream is one of the latest generation of Android phones. It features a 3.2″ screen, full qwerty keyboard, and many other features. Pavel Machek has been massaging getting various features into the upstream kernel, in collaboration with Brian Swetland (Google), and other folks. In his latest email, Pavel posts a driver of “higher quality than usual for staging/” to the staging tree, on the grounds that some cleanup is still required.

KSM. Kernel Shared Memory is a feature in which the kernel is able to scan physical page frames and reconcile duplicates into copy-on-write instances, saving physical memory in situations where the kernel would otherwise be happily oblivious to duplication. This is particular important for systems running large numbers of virtual machines. Various work has gone into design changes to KSM, the latest of which is another version of an madvise version of KSM from Hugh Dickins. Hugh says the patch is not ready for inclusion, but is intended for wider testing and exposure while it is being cleaned up. On a memory related tangent, Dan Magenheimer followed up to the original “Transcendent Memory for Linux” announcement with links to documentation. This is an effort to allow Linux to use flexible memory that might disappear at any moment from underneath it – for example for cacheing purposes.

Performance counters. In an ongoing discussion concerning measurement overhead imposed by the “perf” utility, Paul Mackerras came up with 4 possible solutions, one of which Ingo Molnar (who maintains “perf”) deemed “looks convincingly elegant”. Paul had suggested that “perf” call an execvp with an invalid NULL program name before turning on counters and re-execing with the actual progrma name so as to reduce PLT (symbol) resolver overhead.

In today’s miscellaneous items: David Howells and co are still working to figure out exactly hot the git commit that caused OOM situations did so (he has David Woodhouse running a system reconfigured with mem=1G – rather than its stock 4GB on which it would not run out of memory – for a reproducer, Yanmin Zhang announced a 16% regression in ffsb test cases on JBODs (Just a Bunch Of Disks – typically 13/12 disks in this particular case), a regression fix for x86 from Ingo Molnar, Liqin Chen posted a bunch of cleanups to S+Core, and Gregory Haskins posted fixes to his irqfd/eventfd implementation for use by virtual machines.

Finally today, James Dolan inquired as to the advantages (or disadvantages) of testing a kernel in a Virtual Machine. Overall, the response was positive, even if there are obvious issues testing without real hardware. This author certainly extensively uses KVM for testing quick kernel builds.

The latest kernel release is 2.6.31-rc1, which was released by Linus last week.

Stephen Rothwell posted a linux-next tree for June 29th. Since Friday, he added a new subtree entitled “percpu”, and his fixes tree contains a fix for fbdev. The majority of other trees lost build failures. There are now 131 trees in the linux-next compose.

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