LKML Summary Podcast

Audio: COMING SOON

For the weekend of June 20th, I’m Jon Masters with a summary of today’s LKML traffic.

In today’s issue: Panic, Performance Events, Slow-work, and Timekeeping.

*). Panic. Shoichi Tamuki posted version 2 of a patch intended to fix keyboard LED blinking on panic. Existing systems will call mdelay to handle the reboot timeout post-panic, during which time the keyboard LEDs well blink. When a hypervisor is being used, those mdelay calls of 1 second or more will be implemented as spins, in order to avoid timeout accuracy slips, but the side effect is that the keyboard LEDs won’t blink properly. The patch will call panic_blink_enter() between every mdelay call, and it also fixes up the longer mdelays so that the blinking still occurs.

*). Performance Events. Nils Carlson, Andi Kleen, Eric W. Biederman, Tony Luck, and others, discussed the “Hardware Error Kernel Mini-Summit” followup in which it had been proposed to introduce a new hardware error subsystem. They pondered what (mostly) Andi saw as failings of EDAC and the need for a better way to find such things as which DIMM has failed without doing a binary search removal of individual modules (”the way of the 21st century”). Tony Luck proposed some further ideas for a generic subsystem.

*). Slow-work. Ted Ts’o reported that recent 2.6.35 kernels with an Ubuntu userspace would periodically get into a state in which large amounts of CPU time was spent in the kslowd worker threads. It turned out that this was caused by a change to the DRM/KMS code to pull polling of the display connectors into the DRM core. Reverting a specific commit fixed the issue for Nick Bowler, who had also been experiencing this problem.

*). Timekeeping. Suresh Rajashekara inquired as to what appeared to be a problem with timekeeping on his OMAP1 platform with a 2.6.29 kernel. It seemed odd that certain timers were not expiring immediately upon resume on a system that tries to spend most of its time in a suspend state (waking for 35 milliseconds every 4 seconds, apparently). Thomas Gleixner replied, saying that during such suspend operations, only the CLOCK_REALTIME based timers are kept correct (aligned to real time), whereas others won’t expire the moment the system resumes because there may otherwise be a thundering hurd problem as many timers expire at the point that the system wakes up from the suspend state.

In today’s miscellaneous items:

*). R. F. Burns inquired as to whether it was possible to “write a kernel module which, when loaded, will blow the PC speaker?”. Alan Cox replied that this wasn’t really likely, and in the absence of the root password and proper expertise, “throwing it out of the window or feeding it iron filings will work just as well.”

*). Lai Jiangshan posted a patch removing the use a default write bit with EPT page allocations under KVM virtualization. It wasn’t causing a problem now since get_user_pages is always called with write=1 at the moment.

*). Adrian Hunter posted MMC patches adding support for secure erase, trim, and secure trim – all now variants of erase in eMMC v4.4 cards.

*). Peter Zijlstra noted that the historical uses of perf_disable to prevent NMI races in the PMU code were basically now done per-arch, so he suggested that he would remove perf_disable as it did not seem to be really needed.

*). Christoph Hellwig posted the XFS status update for May 2010, in which he noted several of the important features that lands in 2.6.34 (including new inode and quota flushing code). Christoph also posted a patch (not entirely related to XFS) that removed the 4K stacks option on 32-bit x86 systems as it is deemed “too small” these days, even with now mandatory split IRQ/kernel stacks, given the depth of many kernel call chains.

*). A number of objections to the new automated addition of a “+” to the localversion for modified kernel trees, if no other is set. Mark Hills pointed out that this triggers a lengthy modpost step even when doing “casual kernel development” to test out some simple patch.

*). Dan Carpenter posted a patch that changes the output of kernel oops messages such that the previous “cut here” is replaced with a message asking for the entirity of the oops to be sent in to kernel folks.

*). Zachary Amsden (who has been working on this for some time) posted some TSC cleanup patches and documentation for KVM. This should help resolve many of the issues that have been affecting some TSC users under KVM. On that note, Hagen Paul Pfeifer sent a patch that effectively allows for deliberate speeding-up of time for certain guests for testing use.

*). Huan Ying posted a three-part “Unified NMI delayed call mechanism”, which essentially allows the deferment of certain NMI-time processing until the NMI context has been left. Ingo Molnar prefered that the solution be to re-use the existing unified NMI watchdog code. Sadly, the rest of the thread turned into a bit of a flamewar between Andi Kleen and Ingo.

In today’s announcements:

*). Jeff Merkey announced Open CWorth Libraries 06-19-2010, and ranted about wanting larger stack sizes. He also posted version 2.6.34-06-17-2010 of his “MDB” or “Merkey Debugger”. Nobody replied to any of these threads.

*). Etienne Lorrain announced version 2.8.2 of the gujin GPL bootloader. It contains several bugfixs and improvements – http://gujin.org/

*). James Morris announced the Program Schedule for the Linux Security Summit that will run in conjunction with the 2010 LinuxCon in Boston, on August 9. Further information is available at http://www.linuxfoundation.org/

*). Karel Zak announced that the second util-linux-ng 2.18 release candidate is now available. It contains lots of fixes (e.g. disable DOS mode and cylinders by default now in fdisk). Further information is available at: http://www.kernel.org/pub/linux/utils/util-linux-ng/v2.18/

*). Mathieu Desnoyers announced the release of Userspace RCU 0.4.6. The latest release includes added ARMv7l support. Further information is available at: http://www.lttng.org/urcu/

The latest kernel release was 2.6.35-rc3.

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