2010/01/17 Linux Kernel Podcast
Audio: http://media.libsyn.com/media/jcm/linux_kernel_podcast_20100117.mp3
For the weekend of January 17th, 2010, I’m Jon Masters with a summary of the past week’s (and some holiday) LKML traffic.
Yep, we’re back, and ready for 2010.
In this weekend’s issue: A new format (version 3.0), async page faults, async suspend and resume, feature removal, mod_timer_msec, page allocator, raw_spinlocks, and Linus’ birthday.
A new format. Ever since I started doing these podcasts last May, it’s been a constant struggle to find the time each day to prepare and produce a show. It often takes upwards of an hour to prepare the material and produce the show. I have asked for volunteers, but clearly this will remain a one man effort for the moment. I’ve been sick for the past week (just working on day job stuff) and had a lot of hassles over the holidays that prevented me from pushing updates. It got me thinking about how I can make this show better – easier to produce, and more reliable. I have decided that in 2010 I will try to produce a daily show, but I will only “commit” to a weekly show covering the events of the past week (which will be longer format and produced on Sundays). Days that don’t have a show will be rolled into the next rather than producing multiple episodes that “catchup” the record (so I won’t bother covering a linux-next tree that’s already a week out of date). I would love to do a show every single day, but I need volunteers to help make that a reality (I need time to write on other projects and read a crazy backlog of books). What really matters is that there’s some kind of reference tracking what happened each day. So you’ll just have to make do with some episodes covering multiple days at a go. Unless you want to volunteer with production…
Async page fault. There was some discussion concerning asynchronous page faults. Hirouki Kamezawa originally posted a patch over the holidays that was now in its third iteration. “asynchronous page fault” support is intended to aid highly threaded applications deal with page faults without needing to contend for the per-process (containing multiple threads) mm->mmap_sem. This is achieved through a certain amount of speculative vma handling (knowing that it might be modified or unmapped without the protection of a lock) and falling back to taking the lock if the VMA RB tree is modified while walking it. There were some issues surrounding atomicity with the patches that Hiroyuki posted, while others (including benh) were concerned that some arches make various assumptions about mmap_sem being held. Peter Zijlstra followed up several days later with version 3 of the “speculative pagefault” patch series, making use of RCU for freeing vm_area_struct (VMAs). On yet another VM note, Gleb Natapov posted an updated round of “Add host swap event notifications for PV guest” patches (that allow guests to know about host page faults), and Mathieu Desnoyers posted version 2 of a patch series implementating a new system call that is named sys_membarrier (forces a process-wide barrier).
Async suspend and resume. Rafael J. Wysocki posted some updated benchmarks for his asynchrnous suspend and resume patches, for which he replaced the disk containing rotational media with a solid state device, and enabled KMS. His results suggest that asynchronous resume is 50% faster at suspending (300-350 ms vs. 600-700 ms) and much faster at resuming (1.1-1.2 seconds vs. 4 seconds). That might given Apple a run for their money.
Feature removal. Robert P. J. Day asked about Documentation/feature-removal.txt and whether it was going to be updated (since some items referred to 2005) soon.
mod_timer_msec. Arjan van de Ven posted a patch (intended for drivers) implementating mod_timer_msec, which can be used to set or change a timer for a relative amount of milliseconds. This allows Arjan (and also others too) to remove the need for certain drivers to work directly with jiffies and HZ.
Page allocator. Mel Gorman posted a patch from Corrado Zoccolo that divides freed pages into two classifications – those that have a high probability of being merged with their next-highest buddy, and those that do not. Those pages not likely to be merged in the near future are preferred on the freelist to those that might be mergeable in order to make higher order allocations available using the newly merged buddy pages, and reduce fragmentation.
raw_spinlocks. John Kacur, noting that Thomas Gleixner’s recent work had freed up the “raw_spinlock” name within the kernel for re-use, posted a number of patches converting existing spinlocks over to raw_spinlocks. This is required in the RT tree, wherein all spinlocks are be default converted to a sleeping variety, but for which certain locks must explicitly remain non-sleeping. Locks that must always be real true spinlocks should use raw_spinlock.
Finally today, Linus’ birthday. It was noted by a few posters that Linus’ birthday is December 28th. Linux Journal had an article, and as these things are want to do, Linus’ reply took the conversation off to a tangent about 387 co-processors, to which Avi Kivity added some remarks on the original design.
In today’s miscellaneous items: a new version of kFIFO (Stefani Seibold – and an even newer version on January 14th that is re-implemented and apparently does not require any changes to existing code users of the old kFIFO API), an XFS status update from Christoph Hellwig (who notes that ongoing work includes support for new event tracing code and mkfs.xfs default support for “lazy superblock counters”), a refresh of the jump labeling patches (v4) from Jason Baron, a patch from Dave Jones removing his name from checkpatch.pl (so people stop asking him about it), initial PCI support for Xilinx Microblaze (and a discussion about generic PCI support file locations), a modpost patch implementing support for ELF objects with greater than 64K sections – recall that this has to be handled specially in ELF – for use when compiling a kernel with -ffunction-sections and having e.g. an allysconfig, and a mini-rant from Stefan Richter concerning “Changelog quality” that is worth reading. Finally, Dan williams (the Intel one) is taking over maintainership of I/OAT.
In today’s announcements: LTTng version 0.186o for 2.6.32-rc8 and Userspace RCU 0.3.3 were both released by Mathieu Desnoyers on January 4th. He posted an updated Userspace RCU 0.3.4 on January 10th, that had some additional fixes.
LTP. Subrata Modak announced the December 2009 Linux Test Project release. It included a number of build system fixes for various distributions.
rt-tests version 0.60. Clark Williams announced the latest version of rt-tests on December 29th. It includes a new ‘pip’ (Priority Inheritance stress test) from John Kacur and adds an unbuffered output option to cyclictest for those parsing the output at runtime. The source is available on git.kernel.org.
smatch 1.54. Dan Carpenter announced version 1.54 of his “smatch” static source code checker tool for C programs such as the Linux kernel. His intention is for “smatch” to become “a smarter version of checkpatch.pl”. It includes cool things like a check for DMA use on the kernel stack.
SystemTap version 1.1. David Smith announced the 1.1 release of SystemTap. This includes better support for gcc 4.5 “richer” debuginfo, amongst other fixes. It’s available from http://sourceware.org/systemtap. Frank Ch. Eigler followed up to note that this release also includes a fix for CVE-2009-4273.
util-linux-ng v2.17. Karel Zak announced the latest 2.17 release of util-linux-ng, which contains a number of new features (an fallocate command, unshare command, wipefs command), and updates to libblkid, blockdev, fdisk, and other fixes.
The latest kernel release is 2.6.33-rc4. There was an rc3 too, but that was pretty small “due to the holidays”. 2.6.33-rc4 had few updates, but 40% of those were in DRM (nouveau and radeon in the staging tree, i915 updated too), and Linus called that out as being “unusual”. There were also some bootloader issues on non-x86 systems, but Linus figured “we’ll sort it out”.
Andrew Morton posted an mm-of-the-moment (mmotm) for 2010-01-15-15-34.
Greg Kroah-Hartman posted some stable review patches for 2.6.32.4, 2.6.31.12 (there had previously been a 2.6.31.10 that was replaced with a build fix in 2.6.31.11), and 2.6.27.44.
Stephen Rothwell posted a linux-next tree for January 14th (and announced that there would be none for January 15th). Since Wednesday, there was a new mtd-current tree, Linus’ tree still had a build failure for which he reverted a comment, the net-current tree lost its conflict, and the tip-tree gained a conflict against the kgdb tree. The total sub-tree count increased to 156.
That’s a summary of today’s Linux Kernel Mailing List traffic, for further information visit www.kernel.org. I’m Jon Masters.
