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2010/06/27 Linux Kernel Podcast

July 11th, 2010 jcm Leave a comment Go to comments

Audio: COMING SOON

For the weekend of June 27th 2010, I’m Jon Masters with a summary of today’s LKML traffic.

In today’s issue: Concurrent coredumps, OpenFirmware, and Power management policy.

*). Concurrent coredumps. Edward Allcutt posted, inquiring about placing a limit on the number of concurrent process coredumps that should be allowed to take place on a system. He cited an example Apache-based webserver in which large numbers of CGI processes were crashing, each with a 150-200MB core file that needed writing to disk. He was using a custom patch that would cease dumping cores after a certain number were already concurrently taking place. Roland McGrath and Andrew Morton did not favor this approach, instead prefering either that core dumps would begin to block (but not consuming resources) after a point, or that the blkio_cgroup IO controller be used to limit the IO being consumed. Hiroyuki Kamezawa suggested that distributions like Fedora – which in that case has its own dumping tool called abrt that manages coredumps – could wire up the blkio cgroup prior to beginning the dump process.

*). OpenFirmware. Andres Salomon posted a patch implementing support for making calls into OpenFirmware on x86 OLPC XO systems. The patch works by preserving the necessary page mappings for the OpenFirmware (OFW), which remains in memory at a virtual address. Just the minimum number of mappings are retained, but this does allow calls into the firmware even after Linux has booted. It’s always been interesting to see the XO using OpenFirmware as one of the only x86-based devices doing so.

*). Power management policy. Len Brown posted an RFC patch implementing a new centralized location for userspace to express its power management vs. performance policy preferences to the kernel. In the patch, such expression occurs through the new /sys/power/policy_preference file, which contains 5 different possible levels – ranging from “max_performance”, through “balanced” (the new default), to the “max_powersave” option on the other extreme. The idea is to centralize setting scheduler, cpuidle, governor, and other options.

In today’s miscellaneous items:

*). Dave Chinner posted a 5 part patch series implementing some fixes for emergency filesystem thawing (via sysrq control).

*). Michael Kerrisk posted some man-pages text for the MADV_MERGEABLE and MADV_UNMERGEABLE flags added in 2.6.32 for use with KSM (Kernel Samepage Mapping – the kernel support for detecting duplicate pages in guest virtual machines and mapping them to a single shared page instance).

*). Paul E. McKenney concluded that it was sufficient to turn off the CONFIG_PROVE_RCU option in Fedora rawhide kernels since it’s mostly a developer tool, rather than change licensing or otherwise make it available to non-GPL modules with which it is not compatible.

*). Luis R. Rodriguez posted a script and some documentation to implement some rudimentary ASPM (a PCI extension that allows devices to go to an entirely electrically idle bus state) support. For further information: http://wireless.kernel.org/en/users/Documentation/ASPM

*). Konrad Rzeszutek Wilk posted a 19 part patch series implementing PCI pass-through for Paravirtualizaed Xen guests, using SWIOTLB support.

*). Mike McCormack wasn’t happy with the 32 (NGROUPS_SMALL) group limit on the number shown in /proc/ /status for a given process ID. He and others discussed various ways those who really want more than 32 groups assigned to a process could get the full data through various API changes.

*). Rusty Russell posted the last (hopefully) of his cpumask patches which he says now also means that everyone should be using the cpumask_functions. At least, everyone in kernel is, according to his tests on 32-bit.

In today’s announcements:

*). Mathieu Desnoyers announced that LTTng 0.218 for kernel 2.6.34 is now available. For further information: http://www.lttng.org/

*). Henrik Rydberg announced version 1.0.1 of the mtdev Multitouch Translation Library is now available (releaseed under the MIT license). mtdev does all of the necessary finger tracking pieces in userspace, and separate from the Xorg driver from which it came, as a means to further adoption. This author is still waiting for his Apple Multitouch keypad to work on a Fedora system without having to patch the kernel with a kludge. mtdev is available at: http://bitmath.org/code/mtdev/

*). Len Brown announced the Boston Linux Power Management Mini-Summit will take place concurrently with the Linux Foundation LinuxCon 2010, on the day immediately prior to the beginning of the main events, August 9th. For further information: http://events.linuxfoundation.org/

The latest kernel release was 2.6.35-rc3.

Finally today, Piotr Hosowicz wondered aloud why Linus’ git repository was not being updated, asking if it’s because he’s on vacation. As mentioned before, Linus was indeed on a (well deserved) vacation.

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