Red Hat, Novell To Package Xen

robyannetta writes "Watch out VMware and Microsoft. Here comes Xen, an open-source virtualization for the Linux environment being pushed by Red Hat and Novell. Xen has also joined forces with leading Linux distributors, chip vendors and platform vendors to create a consortium that will more broadly enable open-source virtualization development and deployment." We've covered Xen before, but it's cool to see the momentum behind it growing, as more choice is a Good Thing.

Comments

Giving me a headcrab-ache

[SIGALRM]

Xen has also joined forces with leading Linux distributors

Am I missing something or does this mean Vortigaunts might enter Earth through portals ... wearing Fedoras?

Oh my, it all makes sense now.

USE THiS XEN LINK

[Anonymous Coward]

http://www.cl.cam.ac.uk/Research/SRG/netos/xen/

Uhm...

[Richard_at_work]

'Watch out VMware and Microsoft'? If im correct, Vmware and VPC doesnt require the host operating system to be actually ported to the virtual system, whereas Xen does. This might be fine for specific usage, but its next to useless for what I use vmware for - trying out new and interesting operating systems, configurations or such. The markets may overlap near the top end, but I see no reason why VMware/VPC need watch out, as the main market for these VMs is running Windows, and while there has been a developers port of WinXP to Xen, I severely doubt you will see that in the wild.

Re:Uhm...

[interiot]

From the article...

• Xen does not support Windows today because it uses a technique called para-virtualization to achieve high performance that involves modifying the operating system kernel, Pratt said. However, the debut of virtualization features in next-generation CPUs from Intel and AMD will make it easier to support unmodified operating systems, Pratt said.

• "At that time we will reconsider Windows support," he said.

And more here:

• Full virtualization requires no changes to the guest OS. But it is not well suited for x86 architecture as x86 is not virtualizable. x86 has machine instructions that are termed sensitive. Sensitive instructions will fail without trap when executed in the guest OS. This requires dynamic rewrite of guest OS kernel during run time and shadow system structures which results in a performance hit. Para-virtualization solves the above issues but it requires changes to the guest OS kernel although are required for the Application Binary Interface (ABI) and hence applications can run as they are on the guest OS.

Re:Uhm...

[ScoLgo]

Shatner? Is that you?

Re:Uhm...

[lakeland]

Xen won't run an OS unless that OS has been especially ported to Xen. I.e. it is ideal for running linux, BSD, and not much else. It is also x86 only (I can't use it as a MOL replacement).

It has one huge benefit over VMWare, it is extremely fast. The virtual machine has so close to the performance of the host that it would be reasonable to do such things as: implement a 100% reliable server on your computer and then implement an up-to-date desktop machine inside it. Implement virtual hosting on cheap x86 hardware. Run two distros simultaneously, etc.

Personally I think running a reliable server on the same hardware as your unreliable desktop would be nice. Have the one machine always work correctly for handling mail, printing, web serving, etc. But still up to date.

"Porting"

[vlad_petric]

That's a little bit overstated. For Linux, the changes are a couple thousand lines of code. That's a number I took from their research papers.

But what do you have to change ? First of all, the system has to be made aware that it's not the "top top". Its physical memory is no longer contiguous (you ask Xen for memory pages, and it gives them to you in arbitrary places), it also has to be aware of absolute time that's no longer tick++. Second, you need drivers for the abstract network card and disk. Those are generally easy to write, because you just delegate the real work to Xen. VMWare is already doing something similar with its vmxnet driver for Windoze.

I'd really expect these kind of changes to the OS to be incorporated in the main linux tree, as they mature.

What do you gain from all this ? Well, SPEED. I mean, SPEED. Take a look at their research papers (wrong suggestion for the "I won't RTFA" crowd, but still ...). Their slowdowns/throughput losses (they run Postgres and Apache on a couple of virtual nodes, as opposed to a single, consolidated machine), are negligible (less than 10%). On some configurations they even got performance improvements! At the same time, VMWare and UML do considerably worse.

In general, it's very easy to "virtualize" stuff that's running mostly in user space. As soon as you have considerable OS+I/O overhead, your performance drops significantly. The para-virtualization approach (employed by Xen), pretty much gets you the best of both worlds.

What is Xen? Here you go...

[Erich]

Thought everyone might like an explanation of what Xen does, in comparison to VMware.

VMware works with a host operating system to provide a complete x86 virtual environment for a guest operating system.

Xen is an operating system in its own right. It's a "virtual machine monitor" or "hypervisor". It can spawn multiple guest operating virtual machines.

x86 is not a very good architecture for virtualization. To have a virtualizeable architecture, anything a user-level program can do should behave the same way it would in supervisor mode, or it should trap so the virtual machine monitor can emulate it. x86 has instructions that don't quite follow this guideline -- for instance, you can see what protection ring you are currently in. In supervisor mode, you would get something like ring 0. In user mode, you get ring 3. So an operating system trying to see what ring it was in would get ring 3, but you are trying to fool it into thinking it is in ring 0.

Anyway, Xen modifies the guest architecture. It disallows these "sensitive" instructions and creates some virtual devices that are easier to emulate (like a simple software-programmed TLB). This allows the performance to be very very good, faster than VMware, but it requires you to fiddle with your operating system a bit. Which, of course, is easy to do with Linux.

I see a distribution paradigm

[argoff]

IMHO, this cound change the entire distribution paradigm - for example - if you wanted an email server - you just download the virtual image off the network of a linux system that already has it preinstalled and mostly set up, of if you want a web server/ldap server/dns server - same thing. It is a very nice way to have the best of a full featured linux system while at the same time the xen application os has the minimal stuff nesissary to run what you want.

Re:Virtualization

[IntergalacticWalrus]

VMWare is NOT an emulator, it is a virtual machine. x86 instructions are run natively with some magic to fool the kernel into thinking it is having control of the CPU. Think Xen without the necessary kernel hacking.

The Windows version of Microsoft Virtual PC is a virtual machine, too, while the Mac version is, quite naturally, not a virtual machine but an actual hardware emulator since it runs a different target machine than the host. (Yes, they did give two completely different products the same name.)

Another virtual machine, but running on PPC instead, is Mac-On-Linux.

Xen is the real deal.

[kma]

Disclaimer: I work for VMware, but they don't pay me to post on slashdot.

There are a lot of replies of the form, "Wait a minute, Xen requires that you hack up your guests! What a crock! Typical slashdot hype!" It's true that Xen is more limited than VMware's products, in that you do need to modify guests. However, this doesn't mean that Xen is a joke. (Plex86, for instance, really is a joke, because Kevin Lawton seems to pursue it only in fulfillment of an elaborate VMware-centered revenge fantasy.)

The Xen folks, on the other hand, are smart and mostly serious people. Xen, along with appropriately modified guests, solves some of the problems that our products solve, and for those areas where it fits the bill, it does so in a way that should have lasting performance advantages over full x86 virtualization. What Xen is not, in my opinion, is a virtual machine monitor, for any reasonable definition of VMM. Xen is a microkernel. They don't call it that, because it's hard to get papers about microkernels published these days, but if you think about it, the process of porting an OS to run as a guest under Xen isn't cocnceptually distinct from porting it to run as a personality under Mach or Chorus or whatever. The L4 people didn't even bother renaming their microkernel before repurposing it as a paravirtualization platform.

I think the microkernel analogy helps clarify ones thinking about the promises and limitations of so-called "paravirtualization." Hypervisors are microkernels. In the mid-90's, there was a hope that the whole world would be able to settle on the Mach microkernel. It never happened. Anybody hoping to become the only 'para-hypervisor' will face the same political and commercial challenges.

So to recap: Xen is not a replacement for VMware's products. Xen will probably not take over the world to the degree that its creators would like. Xen is not, however, a joke. The Xen researchers are mostly conscientious, smart people who, fairly enough, would like to see their work have some commercial impact. I really wish they'd stop beating their chests over benchmarks that show them beating a three year old version of our desktop product, though.

Re:Xen is the real deal.

[Ivan the Terrible]

I really wish they'd stop beating their chests over benchmarks that show them beating a three year old version of our desktop product, though.

Does VMware's license forbid its use for comparison purposes? If so, it's up to you (VMware) to change it. The ball is in your court.

If not, why don't you give them a copy to benchmark with? It's not like you'll lose a sale, so the out-of-pocket cost is effectively zero. In fact, it's probably a net gain because of the less-than-favorable publicity they generate. Again, the ball is in your court.

Or, if can't or won't give the s/w away, why don't you publish some benchmarks? Yes, again, the ball is in your court.

Let us (the Greater Slashdot Community ) know what you plan to do.

Re:Xen is the real deal.

[Doodhwala]

The Xen researchers are mostly conscientious, smart people who, fairly enough, would like to see their work have some commercial impact. I really wish they'd stop beating their chests over benchmarks that show them beating a three year old version of our desktop product, though.

All right... so while I accept most of what you have said earlier as quite informative, I do take strong objection to the above statement. You do realize that the research community is forced to benchmark against Workstation 3.x because your EULA in later versions prevent any of us from publishing benchmarking numbers (Look at the Restrictions section in the EULA for Workstation 4.x).

While I understand that there might be commercial reasons behind it, it seems that VMware wants to play in the research field (publish papers at all the top systems conferences) but not allow anyone to try and reproduce what their research claims.

Disclaimer: I have worked on virtualization projects including Xen.