Improvements throughout – what's new in Linux 2.6.25

In association with heise online

Statistics

Data and statistics on the latest versions of the Linux kernel

Linux version	Number of files¹	Lines of source text²	development period	Number of commits³	Diffstat⁴
2.6.20	21280	8102486 (7400843)	66 days	4768	5825 files changed, 262475 insertions(+), 136162 deletions(-)
2.6.21	21614	8246470 (7522286)	80 days	5016	6568 files changed, 319232 insertions(+), 175247

2.6.22	22411	8499363 (7744727)	74 days	6526	7620 files changed, 519591

2.6.23	22530	8566554 (7818168)	93 days	6662	7203 files changed,

2.6.24	23062	8859629 (8082358)	107 days	9836	10209

2.6.25	23810	9232484 (8396250)	83 days	12243	9738 files changed, 777371 insertions(+), 404514 deletions(-)

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Results

Summa summarum 2.6.25

Download the Linux kernel – The new Linux versions are available from servers located in the USA and Europe under the kernel.org domain; numerous German mirror servers, usually make the Linux versions available for download just hours after their release. Linux users, however, should not attempt to download and install the Linux drivers and kernels themselves, but rather they should leave this to the Linux distributors.

Linux 2.6.25 incorporates numerous updates - depending on how they are counted, perhaps more updates than any other version in the 2.6 series, since the number of commits carried out in the source code administration system during the 2.6.25 development cycle was significantly greater than the previous record holder, Linux 2.6.24. In the latter version, however, kernel developers changed a few more lines of code than they did in 2.6.25 when they consolidated the i386 and x86_64 directories with some help from scripts.

However the current Kernel version does not introduce as many conspicuous changes as some of the previous versions in the 2.6. series. The changes in the area of Wi-Fi and the advancement of the Ext4 development will likely prove to be the most important in the long run, but many other updates are also very important – some are long overdue.

2.6.24, with its many new Wi-Fi drivers, necessary improvements to the CFS Scheduler, improved power saving techniques, and other significant updates, provided many important updates that were very noticeable in day-to-day use. Also, Linux 2.6.24 initially had some problems that caused headaches for some users and maintainers of distribution kernels. It remains to be seen if this time the 2.6.25 kernel developers have left the training wheels on.

Trends

Kernel trends: what's new in 2.6.26

Immediately following the 2.6.25 release, the first, approximately two week long phase of the Linux kernel development cycle begins, in which Torvalds integrates more comprehensive changes into the next version of the main Linux kernel development line. This time things could run more smoothly, since developers of the various subsystems are coordinating their intended changes for the next version of the kernel – in this case 2.6.26 – with each other ahead of time in the Linux-next Tree, which has been maintained for some three weeks now. This has already had a positive effect according to Andrew Morton. In the final phase of 2.6.25 development, he wrote that there would be significantly fewer merge conflicts and compiler errors than there were in the same phase of 2.6.24.

The Linux kernel development cycle – Like the Linux Weather Forecast – a "radar screen" maintained by the Linux Foundation – and due to the open development process, along with a deep gaze into the tea leaves, heise Open is in a position to make an educated guess about what new features are in store in the next kernel version...

In 2.6.26 a number of improvements for the Wi-Fi subsystem and the Wi-Fi drivers are in the pipeline. Because the most important Wi-Fi drivers are already part of 2.6.25, what 2.6.26 is likely to offer are numerous little improvements to details. Also, the odd improvement tested in the real-time development branch (RT-Tree) could find its way into the main development line in 2.6.26, as has always been the case with previous kernel versions.

The chances for inclusion of the KGDB kernel debugger are better now than they were at the outset of 2.6.25 development. Ingo Molnar was already prepared to toss it into Linux 2.6.25. But Torvalds, critical of the debugger since its inception, ignored KGDB and pointedly criticised Molnar's attempt to offer KGDB for integration in to the x86 architecture via the developer branch. Torvalds said he would not look at KGDB until developers offered the debugger for integration via a separate git tree. Such a git tree has now been created. Also, developers discussed various details of the debugger's implementation and re-worked certain sections of code that were criticised.

One thing that will likely make its way into 2.6.26 is a change that developers made during 2.6.25 development and then partially reversed, which would deny kernel modules – both open and closed source – access to a central function responsible for initialising the memory subsystem, since modules have nothing to do with that function. Along with the VirtualBox kernel module, the controversial Nvidia graphic driver kernel module uses this function, which means that the Nvidia developers will have to look around for an alternative to ensure that the driver works with the upcoming versions of the kernel. The patch to support the PCI Express power management technology Active State Power Management (ASPM) may also make a comeback in 2.6.26 – developers integrated it into the kernel at the outset of the now concluded development cycle, but removed it again a short time later, due to numerous problems.

As usual, the Kernel Log, which appears regularly in c't and occasionally on heise Open, will report in the coming weeks on the most important new features integrated into the Linux main development line and other developments in the Linux kernel. Among these are the new versions of the – 2.6.x.y – stable kernel series that usually correct some error or other in the first few weeks following a new version release in the main development line that kernel hackers and testers failed to catch and correct ahead of time.

Kernel developers will likely release Linus version 2.6.26 in early July, whose updates will be described as usual in detail in a heise Open feature like this one. (Thorsten Leemhuis thl/c't)

[Appendix: more updates to infrastructure and drivers]

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