LKML Summary Podcast

Audio: COMING SOON

For Monday, September 21st, 2009, I’m Jon Masters with a summary of today’s LKML traffic.

In today’s issue: Optimization, performance events, and trace events.

Optimization. Johannes Buchner posted some comparisons between kernel builds with varying optimization levels, pre-emption settings, and IO scheduling policy as pertained to overall system boot time. Overall, his figures indicated that optimization level and pre-emption setting had “no significant influence on speed”, while “CFQ let [his] system boot several seconds faster”. He posted some graphs on his blog. Of course, these figures are only from a single system, but they may be of interest to some others. Arjan van de Ven was interested that the IO scheduler mattered, given that (s)readahead is supposed to help with this, to which Johannes replied that he wasn’t using readahead for his measurements (CFQ apparently wasn’t improved using readahead, whereas the other scheduling algorithms might have been).

Performance Events. Ingo Molnar posted a merge request intending to rename the “performance counters” to “performance events” in light of the ever-expanding all-encompassing nature of the subsystem formerly known as “performance counters”. The tools remain unchanged (as does the ABI that they rely upon), and the rename is largely symbolic in terms of correcting a “missnomer”, largely done using a script that Ingo also included in his posting.

Trace events. Arjan van de Ven posted to bring up a suggestion that Ingo Molnar had made previously, involving the creation of a TRACE_EVENT_ABI, which would be equivalent to TRACE_EVENT except that it would signal a stable interface. But he was running in to some issues where TRACE_EVENT was being defined differently “all over the place”, leading to “really nasty hack[s]” just to make an alias. He wondered if Steven Rostedt had any clever ideas for making an alias “without fouling up the whole tracing system”.

In today’s pull requests: some DRM fixes from Dave Airlie (containing “the main chunk of the drm changes for 2.6.32″ – Ed Tomlinson wondered what was needed to actually use the R300 3D features), some UBIFS and UBI patches for 2.6.32 from Artem Bityutski, some writeback fixes from Jens Axboe, some x86 fixes from Ingo Molnar, some tracing fixes from Ingo Molnar, some scheduler fixes from Ingo Molnar, some performance counters fixes and updates from Ingo Molnar, some core kernel fixes from Ingo Molnar (including a bunch of RCU updates that came from Paul E. McKenney), some “performance events” patches from Ingo Molnar, some HID fixes from Jiri Kosina, sine trivial fixes from Jiri Kosina, some kbuild fixes from Sam Ravnborg (including kconfig refactoring), some firewire updates from Stefan Richter, some xen updates from Jeremy Fitzhardinge (including a fix for stack protector NX support on 64-bit processors that either don’t have the feature or have it disabled in the BIOS on those PC-BIOS systems), and some ioat/async_tx fixes for 2.6.32 from Dan Williams (the Intel one).

In today’s miscellaneous items: ongoing discussion of the best mechanism for implementing a callback when a swap slot is freed, a fix for a hardware erratum issue affecting AMD 813x rev. B1/B2/etc. parts that won’t generate interrupts when using legacy boot quirks from Stefan Assmann (who continues the fight against legacy “boot interrupts” – thanks!), a fix for a rare case when stable_tree_insert() finds a match when the prior stable_tree_search() did not occasionally causing a page leak from Hugh Dickins, helper functions for data filling of seq_file buffers without directly exposing the internal implementation from Miklos Szeredi (apparently suggested by Al Viro), some concerns about the mmapstress03 test in LTP having some “weirdness” from Geert Uytterhoeven, some wonderings whether wake_up_new_task really needs to play with task priorities from Peter Zijlstra (in reply to comments originally raised by a curious Peter Williams), an “alternative implementation” to handle d-cache aliases in performance counters without having to change how x86 does regular allocations (allowing such architectures to avoid unnecessary vmalloc, but necessitating a difference from e.g. sparc, which does) from Peter Zijlstra, a suggestion that a warning be printed whenever attempting to use kernel headers that have not been installed from Arnd Bergmann, version 2 of an RFC patch intended to allow use of SLQB on architectures that allow memoryless nodes to be installed from Mel Gorman, a patch adding a tracepoint for block request mapping from Jun’ichi Nomura, a patch increasing MAX_STACK_TRACE_ENTRIES from John Kacur (to Ingo Molnar – intended to avoid problems with lockdep running out of entries and falling over), and a discussion of when to perform access checks in fchdir from Trond Myklebust and Jamie Lokier.

The latest kernel release was 2.6.31.

Ingo Molnar pointed out that an earlier regression in tty_open last reported in 2.6.31-rc9 was still occasionally rearing its ugly head in -tip testing. Heiko Carstens reported that the latest git tree occasionally saw the “events” kernel thread running on the wrong CPU(!) on s390 with a default kconfig, but it turned out that this was already in a patch heading “Linuswards” later on in the day (Separately, Heiko posted a patch always showing cpus_allowed in /proc/ /status).

Stephen Rothwell announced that there would be no linux-next tree for the 21st, and possibly the 22nd also as he was “a bit under the weather”.

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