posted by Eugenia Loli on Wed 18th Jun 2003 15:47 UTC
IconToday we host an interview with Andy Tucker, Distinguished Engineer of the Solaris kernel. We talk about the internals of Solaris, the competition and the future of the Solaris OE. The 9th question was answered by Robert O'Dea, Director of Engineering at Sun Microsystems.

1. Why have the other commercial Unixes all pretty much bitten the dust? Is Solaris that much better, or is it just more important to Sun than HP-UX was to HP, AIX to IBM or IRIX to SGI?

Solaris Logo Andy Tucker: I think the most important thing Sun has done to ensure the success of Solaris is simply to remain committed to it. Even in the early days of Solaris, when most Sun customers were still running SunOS 4.x and other companies with UNIX implementations were starting to look at NT, Sun stayed focused on Solaris.

You can also look at some of the "big bets" that were made early in Solaris development. One of the most significant was that of designing in support for multithreading and multiprocessing from the ground up. Doing this work up front allowed Solaris to easily scale on large multiprocessors, and to handle the multithreaded workloads that are increasingly common.

2. Do you think that the proprietary, company-supported development effort that you're a part in has any specific benefits over the Linux kernel's Linus-and-his-henchmen method?

Andy Tucker: The main advantage Sun has is that we can make sure our efforts are well integrated and are focused on the needs of Sun's customers. There's a lot of great stuff available for Linux, but the decentralized development model means that someone who's looking for, say, both a fair-share CPU scheduler and network QoS support has to pull the pieces out of different places, build them into a kernel, and hope they work together. Solaris has these as built-in, integrated components that just need to be switched on.

3. Technically-speaking, what do you think of the Linux kernel and the Mach kernel? Also, how FreeBSD 5.x compares to Solaris?

Andy Tucker: I think they're all fine operating systems, each with their strengths and weaknesses. Mach broke a lot of new ground: it was the first microkernel OS to get widespread use and introduced some basic concepts (such as processor sets) that we've since borrowed in Solaris. Linux obviously has a huge developer base, and as a result there's a tremendous amount of activity and energy around it. FreeBSD (and the other *BSD implementations) are inheritors of the BSD legacy and have been the source of a lot of interesting ideas.

I don't really like to do head-to-head comparisons, since I like to think of OS development as a collaborative exercise. We're all working to improve the state of the art and to make life easier for our users. The open source operating systems are often a source of new and interesting ideas; I hope the developers of those operating systems see Solaris similarly.

4. Solaris has some very complex algorithms. STREAMS, page coloring, and multi-level scheduling are all more complex than what is usually implemented in UNIX kernels. In retrospect, which Solaris features have really paid off, despite their complexity, and which ones have not?

CDE Andy Tucker: I'll note that most modern operating systems incorporate some sort of page coloring and multi-level scheduling algorithms; Solaris is hardly unique in this regard. I think that in most cases the significant work we've done has paid off; the complexity (if any) is usually required to meet the customer requirements. We're also happy to rewrite things if we find a better or simpler way to do something.

On the other hand, there are obviously some features that haven't really succeeded in the customer base, such as NIS+. And there are also some cases where we took a direction with the underlying technology that turned out to be a mistake. An example is the two-level thread scheduling model, where thread scheduling happens both at user level and in the kernel. Although this approach had some theoretical advantages in terms of thread creation and context switch time, it turned out to be enormously complicated, particularly when dealing with traditional Unix process semantics like signals. In Solaris 8, we made an "alternate" version of the threads library available that relied solely on kernel-based scheduling; it turned out to be not only much simpler and easier to maintain, but also faster in almost every case. It particularly sped up Java code, which is obviously important to us. In Solaris 9 (and later) we switched over to the single-level library as the only one available.

5. What do you think about the Cathedral vs Bazaar idea when applied to OS kernels, where the programming model is rather different than than of regular application programs?

Andy Tucker: In some ways the Cathedral vs. Bazaar distinction seems a bit artificial. I don't know about other OS companies, but within Sun we have hundreds of engineers from all over the company working on different parts of the operating system. Many of these people aren't actually part of the Solaris engineering organization; they work on different hardware platforms, or on storage devices, or in the research labs, or on some other product that touches on Solaris in some way. We continuously release the latest code for internal use throughout the development cycle, and do beta tests to get feedback from customers. So in a way we're doing "Bazaar" style development, even though it's commercial product and all developers are Sun employees.

The difficulty with this type of development, particularly on a large complex piece of software like an OS kernel, is ensuring that changes are architecturally consistent, well integrated, and of appropriate quality. This doesn't mean there can't be a large development community, it just means there needs to be some person or persons that are checking proposed changes to make sure they're not going to cause a problem. In Linux, this role is filled by Linus and some of the other folks working with him, who review the changes going into the official kernel base. Within Sun, we have groups of senior engineers who similarly review proposed changes for quality, appropriateness, completeness, etc..

Table of contents
  1. "Solaris Interview, Part I"
  2. "Solaris Interview, Part II"
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