Linux Kernel Development: How Fast it is Going, Who is Doing It, What They are Doing, and Who is Sponsoring It 
The kernel which forms the core of the Linux system is the result of one of the largest cooperative software projects ever attempted. Regular 2-3 month releases deliver stable updates to Linux users, each with significant new features, added device support, and improved performance. The rate of change in the kernel is high and increasing, with over 10,000 patches going into each recent kernel release. These releases each contain the work of over 1100 developers representing over 225 corporations.
Since 2005, nearly 10,000 individual developers from over 1000 different companies have contributed to the kernel. The Linux kernel, thus, has become a common resource developed on a massive scale by companies which are fierce competitors in other areas.
This is the fifth update of this document, which has been published roughly annually since 2008. It covers development through the 3.10 release, with an emphasis on the releases (3.3 to 3.10) made since the last update. It has been a busy period, with eight kernel releases created, many significant changes made, and continual growth of the kernel developer and user community.