How Linux is Built with Greg Kroah-Hartman

Greg Kroah-Hartman, Linux kernel developer / maintainer in the SUSE Labs division at Novell, was recently interviewed by Scott Swigart for the How Software is Built website, and I wanted to highlight a few snippets from his interview.

Linux is scalable

"New hardware accounts for the majority of our changes. We get more processors with more and more cores. We had to do a lot of work to make, 8-, 16-, and 32-way machines run really well, and now we’re running 8000 processor machines really well. The scalability is there, and I actually know of people who have booted larger ones, but we’re not allowed to talk about it."

Linux changes at a rapid rate

We’re at something like six or seven million lines of code, and over 50 percent of those lines of code are drivers. I think 30 percent is architecture-specific stuff, for things like processors and networking. The core kernel is like five percent of the overall code. Those numbers have stayed pretty much the same over the past four or five years. We change something like 5,000 lines a day, which is just scary. Fifty percent of that change will be in the drivers, and five percent will be in the core kernel. In other words, the kernel is being modified everywhere at that rate of change.

I just looked it up, and we add 11,000 lines, remove 5500 lines, and modify 2200 lines every single day.

Intel is heavily involved in the Linux kernel

Intel has come on like crazy this past couple of years, and they’re now one of the major contributors to Linux.

USB 3.0 was sponsored by Intel, and it was shown on Linux first–the first implementation of any operating system. Intel gets their hardware working well fast, and working with the Linux community lets them get it out to developers and other people who are making devices fast.

Some companies actually talk to the engineers really, really well. Intel and IBM are very good at this. They sit down, and they talk to the kernel people once a year. “Hey, this is what we’re thinking of doing. How should we do this? How are we going to implement this?” And they get feedback from us directly. And that’s turned out to be a very, very valuable feedback loop.

I encourage you to read the entire interview. I've highlighted just a few snippets that I found particularly interesting, but he also talks about how the kernel is maintained and the impact of trusted relationships, the Linux Driver Project, the future of Linux, and many other topics. It's a long interview, but it's well worth the time.

Intel is one of the top contributors to the Linux kernel according to the latest Linux Foundation report, which I summarized in a recent post. The Linux Foundation report contains other interesting information about frequency of releases, rate of change and source code size in addition to the information about which companies and individuals contribute. It is also a little long, but well worth reading.