LKML Summary Podcast

Audio: http://media.libsyn.com/media/jcm/linux_kernel_podcast_20090826.mp3

For Wednesday, August 26th 2009, I’m Jon Masters with a summary of today’s LKML traffic.

In today’s issue: CFS, Cpuidle, and Hardware Breakpoints.

CFS. Peter Zijlstra noted that the preempt-rt kernel (also known as ‘-rt’ in this particular instance) runs hardware interrupts and softirqs as real time tasks, concurrent with the task load balancing, which is itself done from a softirq task context. This means that there is likely to be at least one (and probably several) real time task running at task load balance time. Recently, it has been observed that load balancing fails on preempt-rt systems in various subtle ways due to the interaction between RT tasks and CFS as described. Peter “solves” this problem for now by ignoring RT tasks when it comes to calculating the individual CPU load thereby reducing the likelihood for Real Time tasks to bounce around, evacuating “a significant numer” of other tasks as they become runnable.

Separately, Peter, who continues to be one of the strongest voices against the “Offline” scheduler proposal, was joined by Ingo Molnar, who stated, “If you on the other hand were approaching this issue with pragmatism and with intellectual honesty, if you were at the end of a string of patches that gradually improved latencies but couldn’t get them below a certain threshold, and if scheduler developers couldn’t give you any ideas what else to improve, and _then_ suggested some other solution, you might have a point. You are far away from being able to claim that”. Clearly, he’s not a big fan then.

Cpuidle. Arun R Bharadwaj posted version 2 of his patch series implementing cpuidle support for POWER systems, including a sample implementation for the IBM pseries platform. Arun’s tests show improved idle handling with the CPU idle overhead now being a fraction of what it had been with the older pseries_dedicated_idle_sleep loop implementation.

Hardware breakpoints. Frederic Weisbecker replied to yesterday’s posting by K. Prasad of updates to the hardware breakpoint infrastructure noting that he was wrong to request the new API that he had, and that he would instead prefer if the perf tools could selectively arm and disarm existing breakpoints, rather than having their own API to create and manage new ones. His email began, “You will hate me but…”, which is always a good sign.

In today’s miscellaneous items: some networking fixes (smc91x, oom in virtio_net), version 5 of the crashkernel=auto patchset from Amerigo Wang, some tracing fixes fixing a bug in splice_read for the ring_buffer (and allowing rb_get_reader_page to be called by blockable code) from Lai Jiangshan, some vdso32 fixes from Jan Kratochvil, the latest iteration of Rafael J. Wysocki’s asynchronous suspend and resume patches for system sleep state transitions such as suspend to RAM, an update to yesterday’s hardware breakpoint patches from K. Prasad, a fix for a memory leak in IMA from Eric Paris, some thermal management improvement patches (including documentation updates) from Frans Pop, a fix to avoid returning to userspace with the BKL held from within the vt code from Henrik Kretzschmar, a fix to avoid complaints from the perf tools if root owns perf.data from Pierre Habouzit, a module fix for symbol_put_addr such that it uses dereference_function_descriptor on architectures using function descriptors, such as powerpc from Rusty Russell, round 4 of the pending KVM updates for 2.6.32 from Avi Kivitiy (who’s vying with Ingo Molnar for patchcount), version 3 of the per-process OOM killer rework (true per-task oomadj, etc.) patches from Kosaki Motohiro, a fix for unintended panics in the MCE handler code from Hidetoshi Seto, a fix to a sys_umount induced perpetual freeze in the filesystem freeze code, some tracing updates for the forthcoming merge window from Steven Rostedt, and some S+Core updates from Liqin Chen (who seems to have convinced his company to setup a public git server – another awesome sign of a developer who has gotten involved with the community with helpful
assistance and mentoring activities from Arnd Bergmann).

In today’s announcements: 2.6.31-rc7-rt8. Thomas Gleixner announced the latest version of the preempt-rt patch, which is updated to Linus’ latest kernel, includes the previous performance counters crash fix from Peter Zijlstra, and contains two other fixes. There are still known issues with ARM highmem and scheduler load balancing “oddities” for which Peter Zijlstra is working on some magic fixes, as covered earlier in this episode.

Ryo Tsuruta announced the IO Controller mini-Summit of 2009, which will be held immediately prior to this year’s kernel summit. On the agenda are topics that include reconciling the multiple IO controller development projects, extensions to struct bio, and formalizing an I/O tracking and charging policy. There is a website with a wiki for registering (or you can email Ryo). What is not entirely clear is how many of those working on IO controller patches will actually be present at this year’s kernel summit to participate in the debate.

The latest kernel release is 2.6.31-rc7, which was released last week.

Rafeal J. Wysocki followed up to his previous posting of known regression lists with individual replies to many of the outstanding kernel bugs affecting recent kernel releases. Several bugs were subsequently closed. Meanwhile, Darren Hart posted about a trace-cmd memory corruption in Steven Rostedt’s tracing utility. Finally, Eric W. Biederman reported concerns around inotify in 2.6.31-rc6 not noticing deleted files. There has been some rework in this area recently, so it’s quite possible that a regression exists in that code.

Stephen Rothwell posted a linux-next tree for August 26th. Since Tuesday, the uwb tree gained a build failure. The total subtree count remains steady at 141 sub-trees 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.