Avi Kivity is the lead developer and maintainer of the Kernel-based Virtual Machine project, better known as kvm. The project was started in mid-2006, and has been part of the Linux kernel since the 2.6.20 release in February of 2007. kvm is a full virtualization system for x86-based Linux hosts, allowing users to run isolated x86 guest operating systems in virtual machines.

Jens Axboe has been involved with Linux since 1993. 30 years old, he lives in Copenhagen, Denmark, and works as a Linux Kernel developer for Oracle. His block layer rewrite launched the 2.5 kernel development branch, a layer he continues to maintain and improve. Interested in most anything dealing with IO, he has introduced several new IO schedulers to the kernel, including the default CFQ, or Complete Fair Queuing scheduler.

In this interview, Jens talks about how he got interested in Linux, how he became the maintainer of the block layer and other block devices, and what's involved in being a maintainer. He describes his work on IO schedulers, offering an indepth look at the design and current status of the CFQ scheduler, including a peek at what's in store for the future. He conveys his excitement about the new splice IO model, explaining how it came about and how it works. And he discusses the current 2.6 kernel development process, the impact of git, and why the GPL is important to him.

Andrey Savochkin leads the development of the kernel portion of OpenVZ, an operating system-level server virtualization solution. In this interview, Andrey offers a thorough explanation of what virtualization is and how it works. He also discusses the differences between hardware-level and operating system-level virtualization, going on to compare OpenVZ to VServer, Xen and User Mode Linux.

Andrey is now working to get OpenVZ merged into the mainline Linux kernel explaining, "virtualization makes the next step in the direction of better utilization of hardware and better management, the step that is comparable with the step between single-user and multi-user systems." The complete OpenVZ patchset weighs in at around 70,000 lines, approximately 2MB, but has been broken into smaller logical pieces to aid in discussion and to help with merging.

Hans Reiser formed Namesys and began the development of Reiserfs ten years ago. The first release of the filesystem, Reiser3, is part of the mainline 2.4 and 2.6 Linux kernels. The more recent Reiser4 is a complete redesign and reimplementation of Reiserfs, aiming to soon be merged into the mainline 2.6 Linux kernel.

In this interview, Hans discusses his background and how he came to create Namesys and Reiserfs. He looks back at Reiser3, describing the advantages it had over other filesystems when it was released and its current state. He then explores the many improvements currently in Reiser4, describing the plugin architecture and its exciting potential for future semantic enhancements.

Andrea Arcangeli is well known for having completely rewritten and stabilized the virtual memory subsystem in the 2.4 Linux kernel. Many were surprised when Linus Torvalds merged Andrea's VM into 2.4.10, but the new memory subsystem has long since proved itself. Andrea is a 27 year old Linux kernel hacker living in Italy and working for SUSE.

David Weinehall is the maintainer of the Linux 2.0 kernel. Alan Cox [interview] handed over maintainership of the 2.0 kernel over 4 years ago. David explains in his own words:

"In December 1999, a naughty bug that allowed any local user to crash a 2.0-machine surfaced. Alan Cox admitted that he didn't have any time left to work on the 2.0 kernel any longer, and told me that if I wanted to become maintainer for 2.0 and fix this bug (and some other bugs while at it), it was fine with him."

In this interview David talks about his past, and the things he's doing now.

Marcelo Tosatti became the maintainer of the 2.4 stable kernel when he was 18 years old in November of 2001. His first kernel release was 2.4.16 on November 26'th which very quickly followed the earlier 2.4.15 to address an issue with filesystem corruption. Two years later, he has recently released 2.4.23 and plans to soon put the 2.4 stable kernel into maintenance mode, only addressing bugs and security issues.

Living in Brazil, Marcelo currently works for Cyclades Corporation. In this interview he looks at how he became the 2.4 maintainer, the challenges involved, and brings us up to date with the current status of the 2.4 kernel.

Rusty Russell is a Linux kernel hacker living in Australia, working for IBM's Linux Technology Center. He's also a frequent and talented speaker at Linux gatherings. When talking about Rusty in an earlier interview, Andrew Morton summarized, "he's just a really sharp and witty guy - anyone who has attended one of his sessions at a conference will attest to that!"

Well known for his packet filtering efforts, having written both ipchains and netfilter/iptables, he has continued to make an impressive number of contributions to Linux kernel development. A large sampling of his current projects have been merged into the upcoming 2.6 kernel, including futexes, per-cpu counters, hot pluggable CPU support, and a complete rewrite of the in-kernel module loading code.

For a humorous sample of Rusty's wit, one only needs to look to his email signature which reads, "Anyone who quotes me in their sig is an idiot. -- Rusty Russell." Read on for the full interview.

Nick Piggin, a college student living in Canberra Australia, has been working on an anticipatory I/O scheduler for the Linux kernel [story].

When a process reads data from a disk, the default "deadline" I/O scheduler can offer poor performance if a streamed write is happening at the same time. The reason is that many read operations require multiple reads, each reporting a result back before the next can be scheduled. Thus, each of these reads has to wait behind a queue of writes, resulting in the aforementioned performance problem. The anticipatory scheduler solves this problem nicely by pausing for a few milliseconds after each read, "anticipating" the next read request [story].

In this interview, Nick offers much more detail behind the operation of the anticipatory scheduler. His goal is to stablize and tune [story] the new scheduler, aiming utimately for inclusion into the 2.5 development kernel tree as the default Linux I/O scheduler [story]. The latest version of Nick's anticipatory scheduler can be found here in Andrew Morton's [interview] -mm kernel branch.

Ingo Molnar has been contributing to Linux kernel development since 1995 with an impressive list of accomplishments. Most recently his O(1) scheduler was merged into the 2.5 development kernel, as well as much work to enhance the handling of threads. Other highly visible contributions include software-RAID support and the in-kernel Tux web and FTP servers.

In this interview, Ingo explores how he started working on the Linux kernel noting, "it might sound a bit strange but i installed my first Linux box for the sole purpose of looking at the kernel source." He goes on to explain the concepts behind his new O(1) scheduler, and to describe many of his other kernel efforts. This interview was conducted over several months, and covers a lot of interesting ground...

Con Kolivas, a practicing doctor in Australia, has written a benchmarking tool called ConTest which has proven to be tremendously useful to kernel developers, having been designed to compare the performance of different versions of the Linux kernel. He was kind enough to speak with us, explaining how he got started on this project, what makes his benchmark unique, and how to interpret the resulting output. Comparing the 2.5 development kernel to the 2.4 stable kernel, Con says, "a good 2.5 kernel (and that's not all of them) feels faster than 2.4 in most ways and this bodes well for 2.6." The interesting results from his frequent benchmarks back up this statement.

Con also describes his high performance patchset for the 2.4 stable kernel, currently at version 2.4.19-ck9. This patchset adds a number of performance boosting patches ideal for a desktop environment, such as the O(1) scheduler, kernel preemption, low latency and compressed caching. Read on for the full interview...

KernelTrap's first interview was with Robert Love in October of 2001. Since that time, his kernel preemption patch has been merged into the 2.5 development kernel and he's continued to be active on the Linux kernel development scene. He recently agreed to speak with us again.

In this interview, Robert discusses the status of Linux kernel preemption, talks about his recent involvement with the O(1) scheduler and explains his recent VM overcommit work. He also reflects upon Linus' use of Bitkeeper, the future of Linux, and the recent Kernel Summit in Ottawa.

Presently in California working for MontaVista, Robert will return to college for his third year at the University of Florida in late August. Read on for the full interview.

Marc-Christian Petersen originated the WOLK project in March of 2002. WOLK is the Working Overloaded Linux Kernel, a large set of nearly 450 useful Linux kernel patches applied against the current stable 2.4 tree. The project has recently expanded to offer a second 'secure' patchset, this one against the older stable 2.2 tree.

In this interview, Marc-Christian Petersen tells the history behind WOLK and discusses many of the patches included.

KernelTrap has spoken with Peter Chubb who currently works for the Gelato Project. His efforts are presently focused on supporting large disks and partitions, utilizing 64-bits. Regarding the project's focus of improving Linux support for the Itanium 64-bit processor, Peter says, "Back in the days when the VAX was king, there was a general assumption amongst some programmers that `all the world's a vax'. In the Linux world, there's a similar assumption: `all the world's a pentium'."

Peter lives in New South Wales, Australia, with his wife, Lucy, also a kernel hacker, and two daughters. He earned a PhD under the late John Lions, author of the Lions Book. His UNIX kernel hacking experience is with an impressively large number of kernels.

KernelTrap has spoken with Larry McVoy, BitMover founder and primary BitKeeper author. BitKeeper, a distributed source control system, has been adopted by Linux kernel creator Linus Torvalds and condemned by free software icon Richard Stallman.

In this interview, Larry looks back through the years, describing his exposure to computers and Linux. He also discusses the history of BitKeeper, from writing NSElite for Sun (which turned into their still used SCM, Teamware), to his desire to keep Linus from burning out, to the present day solution. The choice to not license BitKeeper under the GPL is also explained.

Larry discusses much beyond Bitkeeper as well, exploring some of his other interests. For the full interview, read on.