"We all wear the brown paper bag on occasion, and with the 'merge maelstrom' during each merge window, I'm quite frankly amazed at how _little_ stuff gets broken overall."
"I re-ran some statistics the other day on our kernel development rate, and changed my formula after Andrew accused me of severely undercounting the rate of change," noted Greg KH during a discussion about the stability of the Linux kernel while undergoing significant changes. He continued, "turns out that as of 2.6.24-rc8 for the 2.6.24 kernel release we did: lines added per day, 4945; lines removed per day, 2006; lines modified per day, 1702". Greg added:
"And note, that is real stuff, not renames or file moves at all, git handles not reporting that. That's for the 99 days that it took to do 2.6.24-rc8 (I need to re-run the scripts now that 2.6.24 is out.) It's fricken scarily amazing that things are still working at all... Just something to make you all sleep well at night :)"
"The latest feature release GIT 1.5.4 is available at the usual places," began Git maintainer Junio Hamano. He continued, "it has been an unusually long cycle. 5 months since the last feature release 1.5.3 was really a bit too long. But I hope it was worth waiting for. Thanks everybody for working hard to improve it." He noted that there were 165 contributers resulting in 684 changed files, included 70,435 insertions and 28,984 deletions.
The Git distributed version control system was originally written by Linus Torvalds in April of 2005 to temporarily replace BitKeeper, which he had been using to manage kernel source code since February of 2002. Junio Hamano took over maintainership of Git a few months later, in July of 2005, and the tool has long since become quite popular outside of even Linux kernel development. Regarding the latest stable release, Junio highlighted some of the changes, including:
"Comes with much improved gitk, with i18n; comes with git-gui 0.9.2 with i18n; progress displays from many commands are a lot nicer to the eye; rename detection of diff family while detecting exact matches has been greatly optimized; 'git diff' sometimes did not quote paths with funny characters properly; various Perforce importer updates; 'git clean' has been rewritten in C; 'git push' learned --dry-run option to show what would happen if a push is run; 'cvs' is recognized as a synonym for 'git cvsserver', so that CVS users can be switched to git just by changing their login shell; 'git add -i' UI has been colorized; 'git commit' has been rewritten in C; 'git bisect' learned 'skip' action to mark untestable commits; 'git svn' wasted way too much disk to record revision mappings between svn and git, a new representation that is much more compact for this information has been introduced to correct this; in addition there are quite a few internal clean-ups."
"Even by the exalted standards of [the] LKML which sometimes seems to make a virtue of misinformation, four wrong statements in twenty seven words is pretty impressive ... I salute you!"
Ingo Molnar summarized his pull request for changes to the x86 architecture bound for mainline inclusion in 2.6.25 noting, "it's not a small merge, it consists of 908 commits from 96 individual arch/x86 developers (!)". He continued, "a number of core files are changed as well: most notably percpu, debugging details, timers, the firewire remote debugging patch and ... the KGDB remote debugging stub in kernel/kgdb.c." He went on to detail the extent of the testing this tree has received, "in the past few weeks tens of thousands of random x86.git bzImages were successfully built and booted on a number of (commodity) 32-bit and
64-bit testsystems - and there has been a fair amount of test exposure on -mm as well." Regarding the remote kernel debugger, Ingo explained:
"We tested KGDB to be merge-worthy within the x86 architecture (the only supported architecture for now) and it's better to have kernel/kgdb.c than arch/x86/kernel/kgdb.c. The code is reasonably clean and the user-space exposure is small - the only real exposure is the decades-old remote GDB protocol. We are happy to fix up any further cleanliness comments that people might have - but we really wanted to start somewhere and get this thing moving. As an added bonus: finally a kernel debugger that can be read without puking too much ;-) [anyone remember KDB?]"
"It's hard to overemphasise how out-of-balance the economics are here. You saved maybe thirty person-seconds by skipping the review and checkpatch steps. But the cost (if this bug had gone into mainline) would be many many thousands times higher than this."
"You are trapped in a maze of twisty little documentation patches, all pedantic."
"As you probably know there is a trend in enterprise computing towards networked storage. This is illustrated by the emergence during the past few years of standards like SRP (SCSI RDMA Protocol), iSCSI (Internet SCSI) and iSER (iSCSI Extensions for RDMA)," began Bart Van Assche, proposing that SCST be merged into the mainline kernel. He suggested that while similar to the STGT project which has been part of the mainline kernel since 2.6.20, "SCST is superior to STGT with respect to features, performance, maturity, stability, and number of existing target drivers. Unfortunately the SCST kernel code lives outside the kernel tree, which makes SCST harder to use than STGT."
SCSI subsystem maintainer, James Bottomley, was not convinced, explaining:
"The two target architectures perform essentially identical functions, so there's only really room for one in the kernel. Right at the moment, it's STGT. Problems in STGT come from the user<->kernel boundary which can be mitigated in a variety of ways. The fact that the figures are pretty much comparable on non IB networks shows this. I really need a whole lot more evidence than at worst a 20% performance difference on IB to pull one implementation out and replace it with another. Particularly as there's no real evidence that STGT can't be tweaked to recover the 20% even on IB."
"I think you'd be impressed at how little I care about this, and how little I value my fellow hacker's legal opinions except for humor value."
Prefacing a series of 196 patches, Greg KH noted, "due to the low level nature of these patches, and because they touch so many different parts of the kernel, a number of the subsystem maintainers have asked me to get them in first to make merging other trees easier." Linus Torvalds agreed and quickly merged the patches into his tree. Greg summarized the many changes:
"They can be broken down into these major areas: Documentation updates (language translations and fixes, as well as kobject and kset documentation updates.); major kset/kobject/ktype rework and fixes; struct bus_type has been reworked to now handle the lifetime rules properly, as the kobject is properly dynamic; struct driver has also been reworked, and now the lifetime issues are resolved; the block subsystem has been converted to use struct device now, and not 'raw' kobjects; nozomi driver is added; lots of class_device conversions to use struct device instead."
Ingo Molnar posted a merge request for the latest git scheduler tree summarizing, "it contains various enhancements to the scheduler - find the full shortlog is below. 96 commits from 19 authors - scheduler developers have been busy again. :-/" He added, "the scheduling behavior of the kernel to normal users should not change over v2.6.24, but there are a good number of new features and enhancements under the hood." Ingo went on to list a number of these new features, including:
"Various instrumentation and debugging enhancements from Arjan van de Ven; Peter Zijlstra's RT time limit and RT throttling code for the RT scheduling class; Paul E. McKenney's preemptible RCU code; refcount based CPU-hotplug rework by Gautham R Shenoy; there's serious interest in running RT tasks on enterprise-class hardware, so Steven Rostedt and Gregory Haskins wrote a large number of enhancements to the RT scheduling class and load-balancer; Peter Zijlstra's high-resolution scheduler tick code; [...] and a good number of other, smaller enhancements."
"Let's get this straight... You're suggesting introducing a pointless, ugly macro into the kernel because of a vim bug? *Plonk!*"
"The release is out there (both git trees and as tarballs/patches), and for the next week many kernel developers will be at (or flying into/out of) LCA in Melbourne, so let's hope it's a good one," said Linus Torvalds, announcing the 2.6.24 Linux kernel. He noted, "nothing earth-shattering happened since -rc8". Source level changes can be viewed via the gitweb interface. A nice overview of all changes can be found at Kernel Newbies.
In a followup email, Linus added:
"Since I already had two kernel developers asking about the merge window and whether people (including me) traveling will impact it, the plan right now is to keep the impact pretty minimal. So yes, it will probably extend the window from the regular two weeks, but *hopefully* not by more than a few days."
"I thought that one could place a printk anywhere without worrying. But it seems that it is not wise to place a printk where the runqueue lock is held."
"I'm happy to announce that I've implemented a Block I/O bandwidth controller," began Ryo Tsuruta, explaining that it was intended to be used in a cgroup or virtual machine environment, implemented as a device-mapper driver. He detailed a token-based implementation in which dm-band passes out to the various groups, "a group passes on I/O requests that its job issues to the underlying layer so long as it has tokens left, while requests are blocked if there aren't any tokens left in the group. One token is consumed each time the group passes on a request. Dm-band will refill groups with tokens once all of groups that have requests on a given physical device use up their tokens." Ryo explained:
"Dm-band is an I/O bandwidth controller implemented as a device-mapper driver. Several jobs using the same physical device have to share the bandwidth of the device. Dm-band gives bandwidth to each job according to its weight, which each job can set its own value to. At this time, a job is a group of processes with the same pid or pgrp or uid. There is also a plan to make it support cgroup. A job can also be a virtual machine such as KVM or Xen."