Kernel Log: An analysis of Linux kernel development
A new edition of a study by the Linux Foundation explains the Linux kernel development process and includes various statistics that demonstrate the kernel's growth rate. It also analyses how much is contributed to the kernel's development by which developers and companies.
The Linux Foundation has released an updated edition of its "Who Writes Linux and Who Supports It" study which offers insights into the development of the Linux kernel. The new edition is called "Linux Kernel Development – How Fast it is Going, Who is Doing It, What They are Doing, and Who is Sponsoring It" and, like the first and second edition, it analyses such aspects as which companies sponsor the kernel's development, how many programmers contribute changes, and how fast the kernel is growing.
The study was written by kernel developer and chief editor of LWN.net, Jonathan Corbet, by kernel developer Greg Kroah-Hartman, who works on SUSE products at Novell, and by the Linux Foundation's Amanda McPherson. Like the first two studies, the current edition is based on kernel version 2.6.11 – immediately after this version, Linus Torvalds migrated the kernel sources to the Git source code management system he had started at that time. In some areas, however, the authors of the study focused on the changes the kernel developers made between version 2.6.30 and version 2.6.35 – which covers the period between the study's second edition and the time of writing of the now released third edition. As before, the three authors used the "Git Data Miner" (gitdm) for their evaluations (access to this link requires the installation of a Git handler).
For the evaluation period, almost 19% of changes were reportedly contributed by unaffiliated hobbyists. In second place were the Red Hat developers with a contribution of over 12%, followed by the Novell developers, who contributed 7%; IBM came in fourth place with a contribution of 6.9%, closely followed by the group of unknowns, with a contribution of 6.4% of changes.
Red Hat and the unaffiliated hobbyists also came out on top in the evaluation of the changes made between the release of 2.6.30 and 2.6.35. Here, Intel managed to push past Novell; the authors also point out that Nokia, AMD, Texas Instruments and Samsung increased their efforts and consequently moved up in the ranking.
Counting the group of unknown developers with the unaffiliated hobbyists in both statistics, it was found that more than 70% of kernel hackers receive payment for their work on the kernel.
The authors also looked into which developers review the code of other kernel hackers before it gets integrated into the kernel – these are mostly the subsystem maintainers. The greatest number of reviews in the currently evaluated period were done by David S. Miller, who maintains the network, IDE and SPARC code. He's followed by John W. Linville (WLAN) and Greg Kroah-Hartman (USB, Staging, Driver Core) as well as Andrew Morton, who handles all kernel areas.
The authors related these figures to the employer figures, which showed that almost 38% of the code is handled by Red Hat developers. Novell came second with over 13%, followed by Intel with just over 9%. In this evaluation, the unaffiliated hobbyists only contributed just under 5%.
The study also explains why these companies, which come from a variety of different backgrounds, support kernel development. IBM, Intel, SGI, MIPS, Freescale, HP or Fujitsu are working to ensure that Linux runs well on their hardware, which is, in turn, said to make the hardware more attractive to Linux users and increase sales. Linux distributors like Red Hat, Novell and MontaVista have a clear interest in making Linux as capable as it can be, say the authors; this motivates them to cooperate even though they compete with each other in the market. Sony, Nokia and Samsung, on the other hand, use Linux in their products; their contributions to the kernel development helps them ensure that Linux will continue to be a solid base for their products in the future.