Main development phase for Linux kernel 2.6.37 concluded
Ten days after releasing Linux 2.6.36, Linus Torvalds has issued the first release candidate of Linux kernel version 2.6.37. This concludes the kernel's merge window – the first phase in the development of a new kernel version during which the kernel hackers integrate the majority of changes into the source code management system of the main development branch.
In the latest merge window, Linus Torvalds has integrated about 9,500 minor as well as major changes for version 2.6.37. According to diffstat, the developers have modified 10,315 files; 1,037,346 lines of source code have reportedly been added, and 560,632 have been removed. Linux 2.6.37 will, therefore, be a version which brings a comparatively large number of changes; the diffstat says that 2.6.36 only contained 582,139 new lines of source code.
In his announcement of 2.6.37-rc1, Torvalds points out that the Linux kernel's core areas no longer use the Big Kernel Lock (BKL) – a bulky locking technology from the Linux kernel's early multi-processor days. Relatively easy to implement at the time, the mechanism locks across subsystems and soon becomes a bottleneck in systems with many processor cores.
As expected, the kernel developers have also integrated "Initial Domain Support" for Xen. This is an important step towards running the Linux kernel as a controlling Xen domain (Dom0). However, Jeremy Fitzhardinge recently pointed out that the kernel is still missing the back end drivers required for Xen Dom0 operation; the developer hopes that these drivers can be integrated into the Linux main development branch in the next development cycle.
As always, numerous drivers have been added or improved: among the new additions is the UAS driver for USB Attached SCSI, which allows fast data exchanges with USB 3.0 storage devices and the driver for Apple's Magic Mouse now also supports the Magic Trackpad. The "Lazy Inode Table Initialisation" feature is designed to considerably speed up the creation of Ext4 file systems. As usual, The H Open will discuss these and dozens of other important new features of Linux 2.6.37 in a "Coming in 2.6.37" mini series.
In accordance with a rough indication Linus Torvalds had made earlier, the latest merge window lasted only eleven days instead of the usual two weeks. This was partially caused by Torvalds travel arrangements and that of many other important kernel developers, who are meeting at the Kernel Summit yesterday and today – an annual meeting where the invited kernel developers discuss and come to agreements on various topics. This year the Summit is in Boston. The Linux Plumbers Conference will follow immediately afterwards and will discuss kernel topics as well as X Server, Udev, PulseAudio and other software components that are important for system operation, but don't usually directly impact users.
With the merge window closed, kernel development has now entered a stabilisation phase of usually eight to twelve weeks during which Torvalds will typically issue new release candidates on a weekly basis. A final release of Linux 2.6.37 at Christmas will, therefore, only be feasible if the kernel hackers work a little faster than they have done recently; at the moment, a final release in January seems far more likely.
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