Slashdot Mirror
Tanenbaum-Torvalds Microkernel Debate Continues
twasserman writes "Andy Tanenbaum's recent article in the May 2006 issue of IEEE Computer restarted the longstanding Slashdot discussion about microkernels. He has posted a message on his website that responds to the various comments, describes numerous microkernel operating systems, including Minix3, and addresses his goal of building highly reliable, self-healing operating systems."
When did we collectively forget that everything has its place...I doubt I'll ever see anything but a monolithic kernel on my desktops. No different than any given OS having its place. Windows and Ubuntu (until something better) will live on my desktops, not on my server. Why can't we just all get along?
Why go fast when you can go anywhere? O|||||||O
yeah, and in that same vein we'd all have Betamax players.
:-D!
I am NOT implying that uKernels are better, I am playing devils advocate.
Not everything that "wins" is the best... Look at Windows
"TVs don't have reset buttons. Stereos don't have reset buttons. Cars don't have reset buttons."
They may not be labeled "reset" but they *do* have them. And, no offense, but I like having a reset button.
You're on to something...you are very close to the cache. Why are we "debating" this when the asnwer seems very clear once one takes a step back: They (the kernels) can exist in harmony, each in its own place. Tanenbaum makes a decent showing of examples about where and why micros are used. This isn't a "which is better" argument. This should be a "where is one better utilized than the other in situation X" debate. That flamewar I could tolerate. Bottom line is that neither will replace the other, at least in a timely enough manner that it is worth wasting time over now.
Why go fast when you can go anywhere? O|||||||O
You-betcha. I honestly think Mr. Tanenbaum is wasting his time in replying to Slashdot. If the last article proved anything, it's that the majority of responders were stuck on the whole "Linus 'won' this over a decade ago, so STFU!" (No one really 'won' the argument, but that's beside the point.)
There were a couple of good replies in there, but they all got drowned out in the noise. Soooo, I think it's a better idea to focus on how Minix might be made a viable OS rather than arguing the same nonsense all over again. As several of the posters here have already proven, they're not reading Tanenbaum's arguments anyway. So why should we expect this time be any different than the last?
Javascript + Nintendo DSi = DSiCade
He also likes to get into flame wars with Linus Torvalds when he gets bored.
Really? And what exactly do you base this on? According to the article, which it's clear that you did not read, Tanenbaum simply had a recent article printed in IEEE Computer and someone on Slashdot posted a link to it, which caused Linus to weigh in with his 2 cents about something that was never directed at him. It sounds more to me like Linus is obsessed with proving that macrokernels are the only way to go. Why does he even care? It's not like Minix is a threat to Linux. If he believes so strongly that microkernels are wrong, he should just let Tanenbaum and company waste their time on them instead of endlessing arguing the same points he made years ago.
A simple way to put the question is this:
If you were given the choice between rebooting your machine every 3 months or so for updates/driver install or never rebooting your machine and but taking a 3-5% performance hit (I think this is what the most efficient uKernels waste on address space switches) which would you choose.
I know my answer. For embedded systems/media center type stuff I don't care about the 3-5% performance hit. I don't ever want to screw with them.
For my computer I don't care about rebooting every 3 months or so. I want that extra little bit of speed.
If you liked this thought maybe you would find my blog nice too:
You would be one of those uninformed pontificators Andy so eloquently railed against.
"For small embedded environments where speed or device support isn't a main concern. Micro-kernels will excel for their stability but take a look around and that's not reality or what we have today. We have lots of different hardware, lots of different interfaces and to manage that all via objects it'll just be extremely large."
And none of that has anything to do with monolithic versus microkernel, except perhaps tangentially. Microkernels do not ask each device driver to be a server all its own with zero code reuse, they use generic servers to wrap drivers for specific hardware while still isolating them from kernel space. This means there's no functional difference to the driver programmer from a monolithic to a microkernel architecture, either way you look at the driver interface and write the necessary code.
"If you think the linux kernel is big the relevant code for this would be numerous times larger. It just pushes the code from the kernel into userspace and you will definitely need more code to manage and access data structure"
Why do you suddenly need more code to the same thing? Andy's point is that when you stop sharing data structures, and instead start passing messages from one discrete server to another through well defined interfaces you reduce the amount of complexity (and therefor code) involved in protecting the coherency of those data structures. You will end up with more interfaces, but thats not necessarily a bad thing. I'd gladly trade all of the critical section protection logic for some nice interface logic. Especially since making the latter work reliably is a hell of a lot easier to do, and gives each subsystem the freedom to rework their internals without requiring me to lift a finger.
"If you can isolate your facets and only plan on supporting X number of devices/platforms/chipsets/etc and don't expect any blazing performance. Microkernels are great. Beyond that? With the rate that technology moves, it just becomes a management nightmare."
There's still no credible evidence to suggest that microkernel performance is that horrible, especially with modern clock speeds. Aside from gaming and large scientific compute clusters, very little being done today on a computer uses any significant measure of their speed. We've already covered how you're totally off base on device support (i.e. its orthogonal to the entire debate), and you throw "management nightmare" out there without bothering to define it, let alone defend it.
Large unix systems are already complex as hell to manage. A lot of that complexity is "hidden" in the kernel, which while fine for desktop users is a big pain for system administrators, and would be exposed for manageability in a microkernel setup.
As for OS X and its performance, its not horribly slow. Especially considering that your complaint almost certainly centers around PPC performance not x86, where it was hampered by lower clock speeds that were not counterbalanced by better IPC in any significant fashion. OS X's memory hunger has little to do with the kernel and lots to do with their operating environment, and all of the gee whiz graphical functionality that OS X brings along with it.
Ultimately though, OSX performance is a success story because on a G3 700mhz with 256M of ram its actually useable. Have you tried running Windows XP on a similar setup? Tried turning all of the eye candy on? Bet you didn't like the way it performed either.
More to the point, ``because it's faster'' has been the bane of Unix. To see that in stark relief, look at the shambles of NFS being in the kernel. Rather than fix the generic problems of providing a user-space nfsd, we saw a race into the kernel for a cheap my-code-only win, plus the horror of system calls that never return. Look at the vogue for in-kernel windowing systems (Suntools, for example) although X mercifully killed that off. Repeatedly we've seen massively complex and invasive kernel subsystems produced, when a generic solution to the problems that going into the kernel allegedly solves would have benefitted everyone for longer.
You've got a problem. You decide to solve it with a kernel extension. Now you've got two problems.
ian
Uhm, I'm pretty sure niche doesn't mean exceptionally widely deployed.
QNX is everywhere, you just don't realize it. ATMs run it, lots of medical equipment runs it, lots of other embedded apps that you don't even think of run it.
The examples Andy cites prove that in fact the microkernel concept has won in every single field where stability has gone beyond being something people wanted to something they demand. As soon as the general public realizes computers don't HAVE to crash, they'll win there too.
You can't seriously believe that running MINIX is going to magically give you expertise that lets you talk about operating system kernel design.
It's apparent from this thread that one needs no expertise whatsoever to talk about operating system kernel design, so running MINIX should if anything overqualify you.
Before we get into arguments or understanding arguments, two most important things to note:
- AST is a prefessor. His interest in doing research and building the best systems for the *future* that he believes in.
- Linus is an engineer. His interest is building a system that works best *today*.
We simply need both. Without pioneering work done before in other OSes (this included failures), Linux wouldn't have been like this today. The greatest reason for its success it not it's doing something cool, but it's doing things that are proven to work.
So who is right? I'd say both. Linus has said this in 1992: "Linux wins heavily on points of being available now."
Linus admits microkernels are "cooler", but he didn't (doesn't) believe in it *today* because none of the available microkernels could compete with Linux as a *general purpose* OS. It's funny how AST listed "Hurd" as one of the microkernels - it totally defeats his own arguments. The fact is Hurd is still not available today despite it was started before Linux.
Many people talk about QNX. Sure, in many cases (especially mission critical, RTOS, where reliablility is so much more important than performance and usability) microkernels are better, but we really shouldn't compare a general-purpose OS with real-time or special purpose OS.
So we go back to the old way: code talks. So far microkernel proponents keep saying "it's possible to do microkernel fast, etc" but the fact is they have never had an OS that could replace Linux and other popular OS that everybody could run on their desktop with enough functionality. There are two possible reasons:
1. Lack of developers. But why? Do people tend to contribute to Linux because Linus is more handsome (than Richard Stallman that is)? There gotta be some reasons behind it other than oppotunities right?
2. Monilithic kernels are actually more engineerable than microkernels, at least for today.
Maybe 2 is actually the real reason?
Think about it.
"Linus 'won' this over a decade ago, so STFU!"
Hey Linus did win this. He was right and NOTHING has changed in the last ten years!
Computers are not that much faster than they where back then and the need for security is no different that then!
Yes I am so kidding. Linus won this because at the time his goal was to get out a Unix clone that ran on the 386 as quickly as possible. Doctor Tanenbaum on the other hand was interested in a Unix clone that would run on cheap hardware and that made a very good learning tool. For his goal Minix was the better system.
Now we live in world of Gigs. It is common to have many gigs of hard drive space, at least a gigabyte of ram, and multigigahertz multi-core cpus. Not to mention that even the cheap built in graphics chip sets would blow the doors off of any video card you could get in 1995.
For all but the biggest FPS gaming freak our computers are fast enough. What we want now is reliability, security, and ease of use. I use Linux every day. I depend on Linux. What I will not do is give up hope on something better than what we are using today. New idea's should be explored.
I am also a little bit disapointed how little respect Doctor Tanenbaum has gotten on Slashdot. Linus compiled the first versions of Linux using Gcc running under Minix. I am pretty sure that Linus read Doctor Tanenbaum's book and probably learned a lot about how to write an OS from it. When it comes to computer science Tanenbaum's name is right up there with Wirth and Knuth. Of course the odds that any of the people that use STFU in a post have ever read Knuth, Wirth, or Tanenbaum is probably not worth measuring.
Even if you are not convinced that Tanenbaum's methods are correct, his goals of a super reliable, self-healing, and secure OS are correct.
See my blog http://ilovecookes.blogspot.com/ for light hearted technical information.
you mean like Tanenbaum (slashdotted, try later) did?
FTFA:
So **PLEASE** no more comments like "If Tanenbaum thinks microkernels are so great, why doesn't he write an OS based on one?" He did.
i don't reall know what you mean by proof of concept
again, FTFA:
It is definitely not as complete or mature as Linux or BSD yet, but it clearly demonstrates that implementing a reliable, self-healing, multiserver UNIX clone in user space based on a small, easy-to-understand microkernel is doable. Don't confuse lack of maturity (we've only been at it for a bit over a year with three people) with issues relating to microkernels.
i know this is slashdot, and RTFA is some kind of mortal sin, but please at least try.
Stop Computers/Cars Analogies on S