LKML Summary Podcast

Audio: http://media.libsyn.com/media/jcm/linux_kernel_podcast_20090830.mp3

For the weekend of August 30th, 2009, I’m Jon Masters with a summary of today’s LKML traffic.

In today’s issue: Discard, IO scheduler based IO controller, and offline scheduling.

Discard. Christoph Hellwig posted a 7 part patch series implementing his latest ponderings on the best way to implement discard support. This is what happens when disk blocks are no longer in use or needed by a filesystem and can be explicitly returned to the disk as such. If the drive firmware is aware of an explicit discard event, then it can intelligently handle garbage collection and management of flash blocks on SSD devices. In Christoph’s latest patches, blkdev_issue_discard becomes a lot more generic and he mentions that he would like to see some progress on the block layer. Regular listeners may be aware of issues with fundamental ATA commands such as TRIM affecting the actual implementation of generic discard support. Christoph references this problem but still wants to get the other pieces sorted.

IO Scheduler based IO controller. Vivek Goyal posted version 9 of his IO scheduler based IO controller patches, as another RFC. These patches have been floating around for some time now, and represent just one of three competing implementations of an IO controller for Linux. They allow applications to be grouped using cgroups and assigned particular limited amounts of disk time and bandwidth resources that they may not exceed. The latest version of these patches contains a number of fixes and ever growing documentation.

Offline scheduling. Gregory Haskins, Rik van Riel, Thomas Gleixner (aka “the usual suspects”) and others continued debate over Raz Ben Yehuda’s earlier “offline” scheduler proposal. In that proposal, Linux would support offlining a CPU and rededicating it to run an exclusive task free from any of the overheads typically associated with maintaining CPU state (for example, free from any of the usual percpu kernel threads involved) and subject to certain limitations. The conversation had shifted away from that proposal though, and by the weekend folks such as Gregory Haskins were wondering whether one might instead (ab)use the nohz tick disabling code to wrap around a specific task running on a given CPU, gaining the benefits of running uninterrupted but without having to perform many other modifications to the task itself. But as others would later point out, there’s more to truly isolating CPUs than running tasks in a tickless kernel environment.

In today’s miscellaneous items: a suggestion from Peter Anvin that msr_safe functions not return a nonsensical value of -EFAULT but instead use -EIO, some early boot fixes and a conversion of PCI init to x86_init for Intel Moorestown support from Thomas Gleixner (and also some platform_setup based patches for Intel Moorestown from Jacob Jun Pan), version 3 of a asynchronous raid6 acceleration through hardware offloading patch from Dan Williams (the Intel one), a fix for kbuild to detect stack protector support when building on x86_64 systems with an IA32 target, the addition of user and system time measurements in task status files from Tatsuhiro Aoshima, some ACPI fixes from Len Brown, some minor tracing updates for 2.6.32 from Steven Rostedt, version 2 of the hardware breakpoints fixes from K. Prasad, a single wireless fix from John Linville (correcting a regression in the ipw2200 firmware loading code), a fix for rpc_task_force_reencode from Trond Myklebust, a divide-by-zero fix in the performance counters code from Peter Zijlstra (who is obviously not quite yet satisfied at finding these bugs), a patch reducing the kernel stack footprint of the firewire core kernel thread from Sefan Richter, a fix for earlyprintk=dbgp from Jan Beulich, some x86 fixes from Ingo Molnar, version 2 of the previously covered “offline state framework” allowing for a choice of the state an offlined CPU will be placed into from Gautham R Shenoy, an update to the module macro comments syncing real-world use of multiple MODULE_AUTHOR statements with inline documentation from Johannes Berg, another iteration of Mel Gorman’s patches implementing multiple free-lists in the percpu structure used by the low level page allocator (now that such allocations are dynamic), and some continuing rambling about the reliability of various kinds of block device and the failure modes thereof impacting data integrity.

In today’s announcements: Thomas Gleixner announced yet another iteration of the preempt-rt kernel patches for 2.6.31-rc7. In the rt8 release, Thomas includes some further fixes and notes ARM highmem, scheduler load balancing, and latency tracer issues as known issues. He encourages everyone to test this latest release in particular since he wants to release a .31-rt within 24 hours of Linus posting the final 2.6.31 release.

Junio C Hamano announced git version 1.6.4.2, the SCM used by the Linux kernel, which contains a number of fixes.

The latest kernel release is 2.6.31-rc8, which was released by Linus Tovards on Thursday evening.

Eric Paris continues to have fun with inotify. Quoting Eric, “Knocking on wood failed. I actually screwed inotify up worse in -rc8 than ever before (2 new regressions including inotify never gets events!!). Sorry to everyone out there trying to use -rc8″. Eric has been firing off patches in mitigation. Several others reported issues with inotify, including Jeff Chua, who claims that the latest patches adding a terminating byte onto name_len break Samba. Meanwhile, Luis R. Rodriguez reported a number of kmemleak warnings related to ACPI, ext4, and tty use.

Stephen Rothwell posted a linux-next tree for August 28th. Since Thursday, the v4l-dvb tree lost one conflict and gained another, the sound tree gained a build failure, and the rr tree lost its conflict. The total subtree count remains steady at 141 subtrees in the latest linux-next tree compose.

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