LKML Summary Podcast

Audio: http://media.libsyn.com/media/jcm/linux_kernel_podcast_20090820.mp3

The UNipexed Information and Computing Service (UNIX) turns 40 this month. How many of us were around back in the days of Woodstock? Not this author.

For Thursday, August 20th, 2009, I’m Jon Masters with a summary of today’s LKML traffic.

In today’s issue: Lazy workqueues, mailing lists, O_DIRECT, and TuxOnIce.

Lazy workqueues. Jens Axboe posted in followup to a previous rant about the number of kernel threads that had been running on his system (all 531 – really – of them). He prefered keeping the workqueue interface rather than redoing it yet again with some kind of wheel re-inventing new scheme. Jens adds lazy workqueues, which behave like the existing code, but create only one core kernel thread per online CPU that shares the responsibility of providing context for all lazy work not otherwise assigned with its own thread.

Mailing Lists. In another mail along the “should we move to vger?” lines, Roland Dreir solicited for opinions on moving the Linux InfiniBand/RDMA mailing list over to vger.kernel.org. Largely, the impetus seems to be that the existing list on openfabrics.org is closed to posts from non-subscribers, and, just like the recent discussion concerning the ARM Linux kernel list, many would prefer to have a list that was open to posts from non-members (especially as that allows easy cross-posting of topics with the LKML).

O_DIRECT loop devices. Jens Aboe and Alan D. Brunelle had a back and forth concerning some metrics Alan had collected in test runs of Jens’ patch, which aims to unifying O_DIRECT handling to allow loopback device data writes to proceed directly to backing storage without hitting the page cache. Alan’s test runs (available as a large PNG) show a huge drop in performance for POSIX AIO random and sequential writes (half way down the graphic). This isn’t unusual for a patch at an early stage of testing and development.

TuxOnIce. What to do? Nigel Cunningham posted to let everyone know that after his most recent attempt to get TuxOnIce merged (apparently, this is “something like the third time” he has tried to do this by now), there had been an interim agreement that he and Rafael would work on getting functionality merged bit by bit. Alas, both are busy with other things and do not have enough time for the effort, and so Nigel proposes three possibilities. First, he’d like to know if someone would like to improve the existing swsusp code (taking bits from TuxOnIce if they deem it appropriate) without help from him. Second, he’d like to know whether someone would take over TuxOnIce maintainership. Finally, he’d like to know if there are any better ideas that have not occured to him.

In today’s miscellaneous items: some multi-node processor scheduling fixes from Andreas Herrmann, some input updates for 2.6.31-rc5 from Dmitry Torokhov, a series of NFS bug reports from Fenggaung Wu in which recent kernels would suddenly return access denied errors and/or cause kerel panics in nfs_release, an eloquently phrased patch to the PCI DMAR code for the case of a DMAR returning all ones from David Woodhouse informing certain BIOS vendors that they had further lowered his already unprintable opinion of closed source BIOSes and BIOS engineers, a patch from Kamezawa Hiroyuki aimed at better aligning percpu counters, a device table update from Mario Schwalbe adding support for Apple models MacBook 5,1, MacBook Pro 5,1, MacBook Pro 5,2, and MacBook Pro 5,5 (Apple has a tendency to use really stupid model numbering conventions and always has), additional support for cut_here in AFS, CacheFiles, FS-Cache and RxRPC from David Howells such that these filesystems and caching services will display some useful diagnostic information as an accompaniement to a BUG() report (for which he also posted a patch implementing disconnected use of cut_here), some error handling fixes from Florian Tobias Schandinat for the framebuffer drivers implementing support for the error code possibly returned by fb_set_par that was being silently ignored by fbmem.c and fbcon.c, a fix to “reservetop” kernel boot parameter handling from Xio Guangrong, a fix from Jan Beulich to the target specifications in arch/x86/boot/compressed/Makefile such that vmlinux.lds is included and will not cause a number of pointless rebuilt files on each kernel compilation if they are already up-to-date, some sound (HD-audio) fixes from Takashi Iwai, some additional wireless patches for 2.6.32 from John Linville, a suggestion from Balbir Singh that his scalability fixes for root overhead in memory cgroup controllers be merged for 2.6.31 rather than holding off to 2.6.32, version 3 of a patch series from Jason Wessel implementing various EHCI and earlyprintk improvements for attached devices, a fix for a theoretical deadlock involving the del_timer_sync inside cancel_delayed_work from Roland Dreier, and some DRM fixes from Dave Airlie.

Finally today, Frans Pop reported a concern that he was getting a cryptic looking error message that related to his PCI hardware not supporting the Advanced Error Reporting (AER) feature of recent devices. It’s unfortunate that the error result from pci_enable_pcie_error_reporting would lead to such an unhelpful error message in the system logs.

The latest kernel release is 2.6.31-rc6, which was released on August 14th.

Krzysztof Halasa posted saying that he believes he has worked out what was causing the strange network timeouts in 2.6.30.5. He believes the problem lies with network desc’s being allocated non-coherently using a streaming allocation that fails on x86 with swiotlb because swiotlb has no concept of a “dirty” flag and so doesn’t know when to flush. Apparently, there is no other fix than converting the allocations over to coherent forms in post-2.6.31.

Dinakar Guniguntala concurred with John Stultz that he was also seeing an issue with recent 2.6.31 RT kernels in which all tasks would end up bound to a single CPU due to some kind of regression in the SMP scheduler behavior.

Eric W. Biederman reported a NULL pointer deference bug in 2.6.31-rc6 with an overrun backtrace containing a recent call to lapic_next_event and
run_timer_softirq.

Andrew Morton posted an mm-of-the-moment for 2009-08-20-19-18.

Stephen Rothwell posted a linux-next tree for August 20th. Since Wednesday, the drm tree gained 3 conflicts while the fsnotify, drbd, tip and the usb trees all lost build failures and conflicts. The total sub-tree count is steady today at 140 trees in the latest linux-next compose.

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