LKML Summary Podcast

Audio: COMING SOON

For the weekend of April 25th 2010, I’m Jon Masters with a summary of the past week’s LKML traffic.

In today’s issue: Linux 2.6.34-rc5, CFS, Firmware, and IPC.

Linux 2.6.34-rc5. Linus Torvalds announced the release of Linux kernel 2.6.34-rc5 on Mon, April 19th 2010 at 4:42pm PDT (Best Coast Time). As he said, “Another week, another -rc. This time there wasn’t some big nasty regression I was working on to hold things up” (refering to the issues with anon_vmas and anon_vma_chains from last week). The latest release includes a number of general fixes, including boot fixes for ACPI parsing, and the usual kinds of driver updates (radeon, amd-iommu, filesystems). SPARC now has ftrace support if you are interested in playing with that. Upon mentioning regressions, Rafael J. Wysocki seemed to fly into action with his usual vigor and post his regular regression summary of issues outstanding since 2.6.33. The current statistics show that the number of unresolved issues has tended to increase over the several weeks leading up to -rc5, with 34 outstanding.

CFS. Mathieu Desnoyers posted version 2 of a patch entitled “CFS fix place entity spread issue”, which is aimed to address an apparent situation in which Mathieu felt that min_vruntime could go backwards and cause large unwanted latencies for certain workloads. Peter Zijlstra disputed that this was happening and Linus, upon testing the patch, using his “favorite non-scientific desktop load” and found that it made things worse in terms of X performance, which was apparently to be expected (according to Mathieu) because Xorg had been getting unfair runtime treatment that was now corrected. This didn’t make Linus particularly happy (from a user experience viewpoint) and meanwhile Mathieu and Peter continued to debate what was happening. Mathieu posted some links to an ELC (Embedded Linux Conference) presentation that he did on this topic at http://www.efficios.com/elc2010 and then later followed up (in an entirely separate thread) with version 11 of his “introduce sys_membarrier(): process-wide memory barrier” that he uses to assist with his userspace RCU implementation, all the while still stranded at San Francisco airport waiting for a means to get back home.

Firmware. Tomas Winkler posted a thread entitled “request_firmware API exhaust memory” in which it was discovered that some performance enhancement work done by David Woodhouse a while back actually caused the kernel to leak memory used for firmware handling, especially in the case that a large number of calls were made to request_firmware, as in the case of Tomas’ code. The issue was that the firmware code was attempting to free pages not allocated with vmalloc using vfree, whereas the underlying pages were actually being allocated and then mapped into linear kernel virtual memory with vmap calls. The fix involves unmapping and then freeing.

IPC. Manfred Spraul posted a three part patch series entitled “ipc/sem.c: Optimization for reducing spinlock contention” in which he attempts to “fix the spinlock contention reported by Chris Mason: His benchmark exposes problems of the current code”. Manfred then summarizes three main issues, including the prominent first issue that the algorithm used by update_queue() has a worst case performance on the order of O(N^2) and bulk wakeups can enter this worst case if they are unlucky. After applying the patch and performing some runs with sembench using 250 threads, waking 64 threads at a time, Manfred reports 1.1% CPU lost spinning vs. 47% before, and 6% of spinlocks spinning vs. 91% before, amongst other statistics.

In today’s miscellaneous items:

* Jon Corbet posted version 2 of an RFC patch series entitled “Initial OLPC Viafb merge”, and noted that he would begin a linux-next tree.

* Yanmin Zhang posted version 5 of a patch intended to implement perf statistics collection in the host of various guest KVM instances.

* Hiroyuki Kamezawa reported an issue with memory compaction support in the mm-of-the-day (mmotm) for 2010-04-15-14-42. He and Mel Gorman discussed it a little. Separately, Mel posted version 8 of the memory compaction patch series, without an obvious fix for the crash issue.

* Justin P. Mattock reported that the issues booting MacBook Pro systems from the previous week seemed to now be resolved in the latest kernels.

* Rusty Russell posted a module patch that causes the module_lock mutex to be dropped when waiting for parallel module loads to complete.

* Don Zickus posted a 6 part patch series entitled “lockup detector changes” that “covers mostly the changes necessary for combining the nmi_watchdog and socklockup code”.

* Stefani Seibold posted yet another (unversioned in the subject line) 4 part patch series that was entitled “enhanced reimplementation of the kfifo API”, and which contained basically a rebase to recent kernels.

* Kyle McMartin posted a patch changing the default file permissions on the kernel provided pseudo file /proc/sys/vm/mmap_min_addr to 0600 from 0644. There wasn’t a huge security issue as writes were already denied by virtue of the fact that CAP_SYS_RAWIO was also required underneath.

* Kent Overstreet posted version 3 of the “bcache” patch series.

In today’s announcements:

* Linux Plumbers Conference (LPC). Ted Ts’o posted a “Call for Tracks”, noting that this year’s conference will take place in Cambridge, MA from November 3-5. The organizers are looking for “problem statements” summarizing “things that could be improved in Linux that cross multiple interfaces or other project boundaries”. For further information about the conference, and to submit ideas, see: http://www.linuxplumbersconf.org/

* git 1.7.0.6. Junio C Hamano announced version 1.7.0.6 of the GIT utility used for version control by the Linux kernel community. The latest version includes fixes for “git diff -stat” overflow, and “git rev-list –abbrev-commit” using the older 40-byte abbreviation format. Junio also announced version 1.7.1 of the GIT utility, which included updates to gitk, the ability to invoke an external command for passwords (GIT_ASKPASS), a new bash completion script (for those who use that), and dozens of other fixes besides. Git is available on the kernel.org website: http://www.kernel.org/pub/software/scm/git/

* hwloc. Samuel Thibault announced the release of hwloc version 1.0rc1, a “hardware locality” utility intended to provide command line support for obtaining information about NUMA memory, shared caches, processor sockets, processor cores, and processor “threads”. For further detail see the project website: http://www.open-mpi.org/projects/hwloc/

The latest kernel release was 2.6.34-rc5.

Andrew Morton posted an mm-of-the-moment (mmotm) for 2010-04-22-16-38.

There was some ongoing discussion of kernel vmalloc performance and a few patches were posted, most recently from Minchan Kim.

Joe Perches asked about the -staging tree review and acceptance process, noting that there are a “number of patches appear[ing] to go unnoticed or
untracked”. Greg Kroah-Hartman followed up explaining that he’s had conferences, travel, and has moved house, and basically asked for a break.
Greg has generally been responsive on the staging tree discussion list in my experience, and there is a lot of work that goes in there.

Greg Kroah-Hartman posted a 2.6.32 stable kernel review patch series comprised from 197 individual patches to the “long term” stable kernel 2.6.32. He also posted a 139 part patch series for the 2.6.33 stable series kernel.

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