LKML Summary Podcast

Audio: http://media.libsyn.com/media/jcm/linux_kernel_podcast_20091103.mp3

For Tuesday, November 3rd, 2009, I’m Jon Masters with a summary of today’s LKML traffic.

In today’s issue: Block IO controller, FatELF, Ftrace, Performance, and Sysctls.

Block IO controller. The ever patient Vivek Goyal, fresh from the IO minisummit in Tokyo, posted the first version of a new IO bandwidth control patchset entitled that “Block IO Controller”. This RFC patch series aims to address the problem of there being no “one size fits all” IO control policy, and the need for different policies to be implemented for different uses. The patch introduces what Vivek calls the blkio cgroup controller, through which a management interface is provided that can be used to switch policies.

FatELF. Eric Windisch posted some example use cases for FatELF that he felt others should know about, in an attempt to counter some of the points made by Alan Cox previously. In particular, it would seem that Eric is into Cloud Computing in a big way and looks forward to having virtual machine images that can simultaneously run on a variety of different hardware. Although there is certainly some benefit provided by FatELF, it wasn’t clear how these problems couldn’t be solved as Alan had suggested – with different directories containing versions of the same binaries for the different arches.

Ftrace. Michal Simek posted to let everyone know that he is currently working on Ftrace support for the Microblaze CPU architecture (an FPGA-based soft core from the folks at Xilinx). In particular, he is looking at function trace support at the moment and how the mcount function is used to record entry into each individual function. He has a number of questions, and Steven Rostedt (the Ftrace author) was happy to help answer a number of them.

Performance. Alex Shi posted with an observation that performance testing had yielded results with a 20-30% drop off in the 2.6.32-rc5 timeframe. This seemed to be due to a cfq-iosched patch from Jens Axboe. Alex attached an example run of perf stat both with and without the patch, showing a clear difference between the two sets of data.

Sysctl. Eric Dumazet recently observed that sysctl table entries were quite expensive, due to a sentinel value added after each one in order to detect and avoid corruption of table entries. Eric noted that the sentinel need actually only contain a couple of pieces of data, and so he created a special sentinel entry struct called ctl_table_sentinel that was smaller in size. This would apparently reduce RAM utilization of such entries by 40%.

In today’s announcements: Userspace RCU. Mathieu Desnoyers posted to let everyone know that version 0.3.0 of his Userspace RCU patches is now available. This is an RCU implementation using the POSIX pthread functions that applications can use to take advantage of the same features as the kernel has done for some time. The latest version removes a function (call_rcu) for which he had provided differing arguments and semantics than the kernel.

The latest kernel release is 2.6.32-rc6. Linus Torvalds announced version 2.6.32-rc6 of the Linux kernel at 12:05pm US Best Coast Time (PDT). In his announcement, Linus noted that there had been a longer gap since rc5, due in large part to the number of kernel developers who have been away at the kernel summit in Japan or traveling to and fro. There was also an ext4 filesystem corruption problem that required additional time, and that had turned out to be due to enabling checksum testing of journal transactions during recovery. Linus thanked Eric Sandeen for tracking down that particular problem. He also seemed pleased at the number of regressions addressed since 2.6.31.

Stephen Rothwell announced that there would be no linux-next tree for November 3rd due to a public holiday in Australia where he is based, which has apparently also has “nothing to do with a horse race in Melbourne”.

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