LKML Summary Podcast

Audio: http://media.libsyn.com/media/jcm/linux_kernel_podcast_20090805.mp3

For Wednesday, August 5th 2009, I’m Jon Masters with a summary of today’s LKML traffic.

In today’s issue: CPUs, devtmpfs, and KVM.

CPUs. Gautham R Shenoy posted an RFC patch series implementing an idle state framework for offline hotplug CPUs. As Gautham points out, when we go into an offline transition state on current systems, we put the affected CPU(s) into a HLT loop (or the equivalent) rather than using the lower C-states that are available. Previous patches have proposed various alternatives – including putting the CPUs into the lowest power C-states available – but the guys at IBM favor giving the user a choice over which state will be chosen. The patch implements a new “available_offline_states” entry in sysfs, from which one can determine a valid low-power state and configure via “preferred_offline_states”.

devtmpfs. Greg Kroah-Hartman reposted “devtmpfs”, which is a patch series originally created by Kay Sievers. Unlike the earlier devfs, this patch series doesn’t attempt to implement device filesystem functionality entirely in the kernel. Instead, the patches provide an implementation that makes life easier for bootstrapping a system by supplying a pre-populated tmpfs filesystem on boot, containing entries for all the initial hardware devices detected. This can be used to boot a system without “complex userspace bootstrap logic to provide a working /dev”. Once devtmpfs is populated, udev takes over and can freely create, manage, and delete any entries it likes as ususal. For those who don’t want to run udev, devtmpfs also offers a cleaner way out.

KVM. Fengguang Wu mailed to let everyone know that Jeff Dike had discovered that KVM pages are being refaulted in 2.6.29. Quoting Fengguang, who cited Jeff, “Lots of pages between discarded due to memory pressure only to be faulted back in soon after. These pages are nearly all stack pages. This is not consistent – sometimes there are relatively few such pages and they are spread out between processes”. Fengguang posted a patch that “drastically reduces” the problem by respecting the referenced bit of all anonymous pages, but suspects that it may re-introduce a previous scalability issue. Discussion continued at some length between the various KVM folks on this one.

In today’s miscellaneous items: a new version 0.12 of the Ceph distributed filesystem from Sage Weil (including several fixes, and some documentation), some networking updates from David Miller (including a lockdep regression that was triggering for a number of people, and was discovered by Ingo Molnar in the previous day’s networking fixes), automatic crash kernel memory allocation from Amerigo Wang (via the new crashkernel=auto boot parameter), some minor s390 updates from Martin Schwidefsky, some OProfile updates from Robert Richter, a suggestion to setup a patchwork (quilt) instance for linux-alpha (although Jeff Garzik cannot have been the only person to wonder if a demonstrated need exists for this), an update to checkincludes.pl from Luis R. Rodriguez that can remove duplicate header inclusions in place (useful, he says for porting “crap” drivers – he also now closes files as soon as he’s done with them rather than keeping file descriptors lying around), conditional support for MSI in sata_nv from Tony Vroon (so far only for MCP55), some build system fixes from Andi Kleen (mcount handling, gold linker support, gcc 4.5 support), an x86 IOAPIC RFC from Cyrill Gorcunov that will only panic on irq-pin binding if needed (i.e. allow failure in the case of PCI), yet another version of the HWPOISON patches from Andi Kleen, version five of the ZERO_PAGE patches from Kamezawa Hiroyuki (with minor fixes), a version 3 of the “security processor” kernel driver from Intel (now with additional support for re-distributing the no-longer-built-in firmware files), and some DRM fixes from Dave Airlie.

Finally today, Dave Airlie expressed some obvious frustration (citing “shitty scripts”) at the lack of verbosity for make V=1 builds. The builds currently fail to display all scripts that are being executed during a build – in particular, Dave Airlie’s case, the ftrace function pre-patching script.

In today’s announcements: SystemTAP version 0.9.9. Josh Stone announced that version 0.9.9 of SystemTAP is now available. It features faster script compilation, improved userspace probing, support for new DWARF_OPs, self-monitoring markers, enhaced variable access, new SNMP tapset, new dentry tapset, bug fixes…and much more.

linux-2.6.31-rc5-tr1.1. John Kacur announced that he and Clark Williams had put together an unofficial preempt-rt kernel release while Thomas Glexixner was out at summer camp (Thomas volunteers every summer with a local camp).

The latest kernel release was 2.6.31-rc5, which was released over a week ago.

Kosaki Motohiro experienced a “poison overwritten” issue with -rc5, which was triggered by the netdev SKB allocation code, but was not able to reproduce it.

Stephen Rothwell posted a linux-next tree for August 5th. Since Tuesday, the tree gained a few minor conflicts, and remains steady at 138 sub-trees.

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