LKML Summary Podcast

Audio: http://media.libsyn.com/media/jcm/linux_kernel_podcast_20090806.mp3

For Thursday, August 6, 2009, I’m Jon Masters with a summary of today’s LKML traffic.

In today’s issue: AlacrityVM, blk-iopoll, CPU features, PCI Identifiers, Performance Counters, and Tux3.

AlacrityVM. Michaeal S. Tsirkin replied to Gregory Haskins’ announcement of the “AlacrityVM” (which is a fork of KVM) with a suggestion that the Alacrity folks work to start merging with the host side of the project, copy the kvm lists on development, and perhaps update the comparison graphs between KVM and Alacrity to reflect a more “apples to apples” comparison.

blk-iopoll. Jens Axboe posted a patch series implementing a polled completion API for the block layer, with the hope of targeting a merge in 2.6.32. As he puts it, “basically this implements NAPI for block devices, and much of the core is essentially lift from there [the network code]“. Jens has seen good performance results on SSD devices, reducing the interrupt rate a lot (for example, a 28% reduction on a fast box doing 50k IOPS – even with interrupt coalescing support in the hardware being enabled), but up to 95% fewer interrupts on a slow box doing 30k IOPS). Sounds like fun, and was hinted at in the recent “state of the kernel” address at this year’s Linux Symposium.

CPU features. Kevin Winchester noted that his AMD64 system incorrectly reports having X86_FEATURE_LAHF_LM, which the CPU does not actually support (as evidenced by test code which fails with an “illegal instruction”). He tracked this down to an AMD errata that states that the BIOS should program an MSR to indicate that this feature is present, which it might be erroneously doing in his particular case. He suggests that the kernel could automatically remove this feature flag from early Athlon 64 processors known not to support it.

PCI Identifiers. Dave Jones noted the inconsistent approach to handling pci_ids.h, a file containing global PCI identifiers. Officially, this file is supposed to only have entries for drivers that need to share a PCI ID with other drivers (for example, for multi-port cards or alternative drivers), but it has turned into a kind of free-for-all, that Dave aims to fix with a comment explaining when to add new entries to this file.

Performance counters. There were a number of updates and patches to the perfcounters code. These included symbol parsing fixes, reporting fixes, and other updates from third parties. Included amongst these was a patch from Frederic Weisbecker implementing support for ftrace event record sampling.

Tux3. In continuing discussion of the tux3 filesystem, and its future, Daneil Philipps had mentioned how he is more likely to put greater effort into tux3 merging if invited to do so. Otherwise, he says, “if we are not invited to merge, nobody has any cause to complain about progress slowing down”. This caused Ingo Molnar to send a lengthy reply politely explaining that in his 14 years of Linux hacking, he had never seen nor had such an invitation. Linux doesn’t work this way, but instead relies upon people requesting to merge.

In today’s miscellaneous items: version 4 of the trace events for the page allocator patches from Mel Gorman, a patch from Li Zefan allowing one to specify which filter type should be used for TRACE_EVENTs (existing support allowed only customized filters for static and dynamic strings), some test-for-null kmalloc/kzmalloc checks added in PowerPC from Julia Lawall, a minor update to the CPU topology documentation from Andreas Herrmann (adding mention of new attributes for the recent mutli-node processor support), a suggestion from Joe Perches that the MAINTAINERS file more prominently mention the linux-arm mailing list (which Russell King had previously suggested he saw no signs of people moving to), a patch killing the BKL in compat ioctl handling from Arnd Bergmann, a number of /proc/kcore cleanup patches (6 patches actually) from Kamezawa Hiroyuki aimed at removing many per-arch hooks and supporting e.g. VM hotplug, a lengthy question email concerning the correct way to handle DMA and cache on ARMv7 systems from Laurent Pinchart, a patch implementing __[un]register_chrdev() from Tejun Heo allowing one to specify a subset of minor numbers to register and unregister (used by the ALSA OSS cleanups), a new ALS (Ambient Light Sensor) device class in sysfs from Zhang Rui, some tracing fixes for 2.6.32 from Frederic Weisbecker, version 2 of the “crashkernel=auto” patches from Amerigo Wang, some input updates from Dmitry Torokhov, some more DRM fixes from Dave Airlie, callchain support in performance counters and allowing performance counters to access user memory at interrupt time for PowerPC from Paul Mackerras, a request to track down a problem with shmem and TTM from Thomas Hellstrom, and a patch implementing devtmpfs_wait_for_dev() from Mind Lei that builds upon yesterday’s re-posting of devtmpfs and allows the kernel to generically wait for a root device to appear without polling and using other hacks. A number of people have now noticed that one needs to set CONFIG_SYSFS_DEPRECATED_V2 on recent RT kernels if testing on e.g. older Enterprise Linux distribution releases, such as RHEL5.

The latest kernel release is 2.6.31-rc5, which was released over a week ago.

Andrew Morton posted an mm-of-the-moment for 2009-08-06-00-30.

Stephen Rothwell posted a linux-next tree for August 6th. Since Wednesday, Stephen has added support for signed next-yyyymmdd tags, and three minor conflicts were addressed. The tree continues to have 138 sub-trees.

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