Kernel Summit 2005: Virtualization [LWN.net]

From LWN's 2005 Kernel Summit coverage.

Rik van Riel and Chris Wright discussed virtualization. This is currently a hot topic, and several OLS sessions will be dedicated to it in the next few days. At the kernel level, however, it seems that there are not a whole lot of issues which need to be resolved.

Virtual hosts may have multiple virtual processors; they will schedule processes between them. The physical host may also have multiple processors, and it will be performing its own scheduling. Since the two levels know little about each other, scheduling imbalances can result. Xen does a certain amount of "rotating" processes around to deal with this problem. Despite being discussed for a while, this issue does not appear to be particularly serious.

It was pointed out that the various virtualization implementations (Xen and user-mode Linux in particular) have their own virtual buses, virtual drivers, etc. Might there be some benefit in merging them? Perhaps, but the amount of code involved is quite small.

Merging Xen. The Xen patches create a completely new architecture for the virtual machine. There have been objections to this approach; it looked like a maintenance problem, especially as Xen is ported to more real architectures. So the patches are being reworked, and the arch/xen directory is going away. Stuff which is truly specific to Xen will find its way into the drivers or host architecture directories. With these changes made, opposition to the merging of Xen should be much reduced.

Linus had to ask: is anybody actually using Xen? The biggest users are, as expected, in the virtual hosting business. Most of them are still in relatively early evaluation stages - Xen is a young technology. Xen is also heavily used by people who want to play with multiple distributions or otherwise need sandbox systems to work with.

Index entries for this article
Kernel	Virtualization
Kernel	Xen

to post comments

Virtualization

Posted Jul 19, 2005 6:52 UTC (Tue) by Klavs (guest, #10563) [Link] (1 responses)

Did anybody talk about the Vserver project? (it's similar to BSD'ish jails), except with several advantages IMHO.

I believe Rik Van Riel, has been involved in the project at one point.. and I sure would like it in the kernel ;)

http://linux-vserver.org/

Virtualization

Posted Jul 19, 2005 13:54 UTC (Tue) by riel (subscriber, #3142) [Link]

I have been involved with vserver, but gave up after realizing a few drawbacks:

1) every kernel subsystem needs to be virtualized
2) you cannot load different kernel modules in different virtual machines
3) if you have an exploitable kernel bug, every virtual machine is compromised
4) since there is no virtual machine abstraction, installing and managing the virtual systems is very different from the way normal systems are managed

With Xen, there is a much better isolation between virtual machines, and virtual machines can be managed in a way much closer to the way normal machines are managed.

Is anyone using Xen ?

Posted Jul 19, 2005 9:46 UTC (Tue) by copsewood (subscriber, #199) [Link] (2 responses)

I'm currently using User-Mode Linux as a general purpose server, hosted by Bytemark. I have also used UML experimentally. I am interested in using virtualisation technology to support student project work, so that students can learn by having root access to a machine which can be setup and destroyed on the fly, without this interfering with other uses of the physical host. User-mode Linux is currently easier to set up for this kind of purpose, but Xen promises much better performance, particularly when new silicon proposed by Intel and AMD becomes available, with specific support for virtualisation. Running a set of servers, e.g. apache, sendmail, mysql in different VMs offers better sandboxing, as a security failure in one VM should be less likely to result in knock-on security breaches elsewhere, as would occur in a conventional host running multiple software servers.

So I think Xen is likely to become a very significant development, for a number of reasons, and the sooner it has mainstream kernel support, the easier it will be for potential users to get started with it.

Is anyone using Xen ?

Posted Jul 21, 2005 3:25 UTC (Thu) by Blaisorblade (guest, #25465) [Link] (1 responses)

> Xen promises much better performance, particularly when new silicon proposed by Intel and AMD becomes available, with specific support for virtualisation.

This is well-known, but I'd like to point out that even UML is going to take advantage of that new silicon, and even a lot more than Xen I think. There's a lot of ongoing work at Intel on this, and you can read about this on the 2005 Linux Symposium Proceedings, in the talk by Jeff Dike.

Is anyone using Xen ?

Posted Jul 29, 2005 14:59 UTC (Fri) by markwilliamson (guest, #26407) [Link]

VT / Pacifica combined with Xen is an interesting topic.

Vanilla Xen gives you near native performance in virtual machine
*already* - hardware extensions aren't going to provide any immediate
improvements for OSes that run natively on Xen (Linux, BSD, etc) because
you can't really do better than the unvirtualised performance.

The real benefit of hardware support for virtualisation in Xen's case is
that it will enable *unported* operating systems to run, and achieve
reasonable performance. The primary benefit will be the ability to run
Windows. You'll also be able to run old, unported versions of Linux on
Xen in order to migrate old servers completely onto Xen with no
configuration changes.

Typo

Posted Jul 19, 2005 15:46 UTC (Tue) by nstraz (guest, #1592) [Link]

The last sentence in the first paragraph has a typo:

"At the kernel level, however, it seems that there are not a whole of issues which need to be resolved."

I think it should read:

"At the kernel level, however, it seems that there are not a whole lot of issues which need to be resolved."

We'd like to use Xen

Posted Jul 20, 2005 8:14 UTC (Wed) by eskild (guest, #1556) [Link]

We currently use VmWare for virtualizing a number of internal servers; our intraweb, bugzilla, etc. VmWare is quite nice, but the host machine gets loaded pretty heavily with only few VM's running, and VmWare does cost real cash. Xen would be really nice here.

In fact, I've even considered experimenting with Solaris/X86, since it has (apparently) decent vitualization support, although it does seem a bit complex to manage.

So, while we don't use Xen yet as we don't consider it mature enough, we certainly will give it a hard look once 3.0 hits the streets.

Virtualization

Posted Jul 22, 2005 12:40 UTC (Fri) by csamuel (✭ supporter ✭, #2624) [Link]

We're experimenting with Xen for use in Grid computing where we need to build a gatekeeper machine in front of various HPC clusters to run the various versions of Globus that the different grid projects need, along with development versions. I think we're up to 7 at the moment, assuming there's just a single cluster behind it.

Using Xen means we should be able to run this all on a single box, and so far it's looking pretty solid (i.e. it works and we've not seen a crash, asides from when someone tried something a little brave with LVM snapshots, but that may not have been Xen related).

All good fun!
Chris

Kernel Summit 2005: Virtualization

Posted Aug 23, 2007 1:06 UTC (Thu) by marraco (guest, #46950) [Link]

Support for many simultaneous users on ONE pc NOW.

Is only needed the capability of give exclusive access to selected monitor, keyboard, and mouse to a given virtual machine. And obvious "need to have" feature, that it does not have.

and I want it on Unbuntu, please.