Counting Contributions: Who Wrote Linux 3.2?


Once again, it’s time to take stock of the contributions to the Linux kernel. The Linux Foundation has released another report on the speed of Linux kernel development, as well as who’s doing the work and what companies are sponsoring development. Since tracking has began, nearly 8,000 developers from just shy of 800 companies have contributed to the kernel.

The report carries a pretty hefty title, “Linux Kernel Development: How Fast It is Going, Who is Doing It, What They are Doing and Who is Sponsoring It” It was written by LWN’s Jon Corbet, Linux maintainer and Linux Foundation fellow Greg Kroah-Hartman, and Linux Foundation vice president of marketing and developer services, Amanda McPherson.

The report is current up through the Linux 3.2 release, and emphasizes development since the 2.6.36 kernel.

Even at 20 years old, the kernel is still growing. The 3.2 kernel weighs in at more than 15 million lines of code and more than 37,000 files. The 2.6.36 kernel was released in October of 2010, and was 13,422,037 lines of code, and 34,317 files.

Doing the Work

According to the report, more developers contributed to the 3.2 kernel than any other. There were 1,316 developers from 226 companies contributing to the kernel.

But it’s a small number developers doing most of the work. The report says “approximately 1/3 of the developers involved contribute exactly one patch. Over the past 5.5 years, the top 10 individual developers have contributed 9% of the total changes and the top 30 developers have contributed just over 20% of the total.”

David S. Miller claims the top spot for changes, with 1.2% overall. Al Viro, Takashi Iwai, Ingo Molnar, and Tejun Heo are the top five. That’s starting with 2.6.12 – if you look at the period from 2.6.35 through 3.2, you see a slightly different picture. Mark Brown is in the top spot, with 1.3% of changes. Thomas Gleixner, Joe Perches, Chris Wilson, and David S. Miller are the rest of the top five for that period.

If a name or two seems suspiciously absent, it’s because they’re busy looking at other people’s work. According to the report, “we are seeing a similar pattern with a number of other senior kernel developers; as they put more time into the review and management of patches from others, they write fewer patches of their own.” Merge commits, it goes on to say, where a set of changes is merged with another, are not counted in the report. Linus Torvalds, of course, generates quite a few of these.

Who Pays?

So who’s paying for all this, then? Well, as always, the largest percentage of changes (16.2% of changes since 2.6.36) are not sponsored by any employer. The top identifiable employer is Red Hat, with 10.7% of changes. Intel is now second, with 7.2%, Novell third with 3.3%, and IBM comes in fourth with 3.7%.

Texas Instruments, Broadcom, Nokia, Samsung, Oracle, and Google trail behind in the top 10.

And then there’s a name that you really don’t expect to see, with 1.0% of the changes since 2.6.36. Microsoft, yes Microsoft, comes into the picture.

This isn’t all that surprising – Microsoft has supported work for Hyper-V support in the Linux kernel. Microsoft hasn’t suddenly developed an overwhelming love and fondness for Linux – but their customers have and Microsoft is helping to ensure they can offer Linux support when necessary.

Our Beloved Kernel Overlords

All that code that goes into the kernel? It goes through the maintainers, who check the code and sign off if the code can be included in the kernel. That, too, is a lot of work and the report takes note of the reviewers as well as the folks doing the patches.

Greg Kroah-Hartman has the most non-author signoffs going into the kernel since 2.6.35 with 5.8%. Next is David S. Miller, then John W. Linville, Linus Torvalds, and Mauro Carvalho Chehab.

It’s interesting to note that Red Hat employees sign off on nearly 40% of the code that goes into the kernel. Novell is at 13.4%, but that may drop heavily now that Kroah-Hartman is a fellow with the Linux Foundation. Intel signs off on 6.6%, and IBM employees signed off on 4.8%.

Want to see a copy of the full report? Grab it at the Linux Foundation’s Publications Website (PDF). It’s an interesting, and short, read.

It also is worth noting that, 20-plus years in, Linux kernel development looks as healthy as ever. The kernel keeps improving and picking up new contributors with every release. More and more companies find it worthwhile to use, and contribute, to Linux every year.