Linux kernel: 13 million lines, over 5 patches per hour

The Linux Foundation has published its third annual report about Linux kernel authorship. The statistics included in the paper illustrate growth trends in the kernel development process and provide insight into how the labor is distributed among individual contributors and corporate sponsors. The kernel has seen modest growth in its base of contributors over the past year, though the rate of development has seen a marginal decline.
The latest version of the Linux kernel currently consists of approximately 13 million lines of code across over 33,000 files. The rate of development peaked with version 2.6.30 last year, which saw an average of 6.40 patches per hour. The rate declined to an average of 5.30 patches per hour in version 2.6.35.
The Linux Foundation attributes the decrease to a shift in focus from heavy development to stabilization on major components like GEM and ext4 that are reaching maturity. The merging of the staging tree into the mainline kernel (read our coverage of 2.6.28 for more details) inflated the volume of new code that was added last year, thus contributing to the appearance of a decline in activity this year. An informed analysis of the statistics indicates that the Linux kernel development community is still healthy, vibrant, and diverse.


The Linux Foundation report highlights the kernel's top individual and corporate contributors. Between version 2.6.30 and 2.6.35, approximately 19 percent of kernel development was done by independent contributors with no corporate affiliation. These volunteers collectively contribute more code than any single corporation that funds kernel development. The undisputed top corporate contributor is Red Hat, whose employees are responsible for 12 percent of the kernel changes that were made between .30 and .35. The next most prolific corporate contributors during that time period are Intel with 7.8 percent, Novell with 5 percent, and IBM with 4.8 percent.
Although Google uses Linux as a base for its Android and Chrome OS mobile platforms, the search giant's number of contributions over the past year are somewhat low relative to other mobile companies. Google's contributions account for 0.7 percent of the changes made to the kernel between .30 and .35. By comparison, Nokia's contributions represent 2.3 percent of the changes during the same period. Texas Instruments contributed 1.5 percent and Samsung contributed 0.6 percent.


These numbers are based largely on commit count and don't necessarily provide a crystal clear representation of a corporate contributor's significance in the Linux ecosystem. It's worth noting, for example, that despite a low commit count over the past year, Google employs some key kernel developers like Andrew Morton and Ted Ts'o.
Although a lot of the work on the kernel is being done by a small handful of companies, the Linux Foundation estimates that over 500 total companies are participating in Linux development in some capacity. Novell, which is undergoing a pending acquisition by Attachmate, is one of the most active participants. It's unclear if Novell's prolific kernel activity will continue in the coming year as it is integrated into Attachmate's business. We might see a decline in the numbers in next year's report if Attachmate doesn't share Novell's commitment to upstream kernel development.
Readers might be surprised to learn that Linux kernel creator Linus Torvalds is not among the top individual contributors. The Linux Foundation says that this is because Torvalds (who is employed by the foundation) spends an increasingly significant amount of time managing development and merging contributions from other developers rather than developing new features.


The kernel subsystem maintainers individually account for most of the effort to merge contributor patches, however, as they play a more direct role in reviewing the code that enters the kernel. Red Hat is the most prolific code reviewer, accounting for roughly 37 percent of all patch signoffs. Red Hat's David S. Miller (who is known for his work on the network stack and his role in porting Linux to SPARC) accounts for almost 11 percent of total patch signoffs by himself.
As the Linux Foundation concludes in its report, the Linux kernel is one of the biggest and most successful open source software projects ever. Linux's growing dominance in the consumer electronics market is attracting more corporate contributors. For additional details, you can refer to the complete report, which is available for download from the Linux Foundation's website.