A look at Xen related development and how the implementation works in Fedora Core 4 along with some information on the development plans.
Xen in Fedora Core 4
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good technical description of what Xen is and what it can do.
Not a lot of pretty pictures or flowery language, just lots of good info. Be interesting to see what 3.0 brings and also what Intel/AMD’s hardware support will offer.
Also, Xen runs only on x86 systems with 686 processors or better, though ports to x86_64 and other processors are in progress.
Got it on SuSE 9.3 x86_64.
i still dont get it. so whenever xen is added to linux? linux will have to talk to xen instead of the hardware?? is this like hardware abstraction?
It’s a hypervisor. Basically, it’s a program that allows you to run multiple operating systems on a single machine. It’s similar to VMWare, with a few major differences.
1 – It doesn’t work on unmodified operating systems. Yet. Xen requires modifications to the guest operating system – essentially, you port the operating system’s kernel to Xen, with drivers for Xen’s devices.
2 – It’s much faster. The modifications than Xen requires allow it to bypass a lot of the hardware and CPU emulation that VMWare (or VirtualPC, or similar) have to do, so there’s a lot less overhead involved.
3 – Unlike VMWare Workstation or VirtualPC, it’s not intended for desktop operating systems. It’s more geared towards servers, like VMWare’s server versions.
I wonder how long it’ll be before we see the hosting industry dropping products like Virtuozzo for Xen ?
It’s much faster. The modifications than Xen requires allow it to bypass a lot of the hardware and CPU emulation that VMWare (or VirtualPC, or similar) have to do, so there’s a lot less overhead involved.
Somehow this sentence lacks quantitative logic. That Xen does not have these overhead does not mean e.g. VMware automatically have a lot of them.
The need to trap privileged CPU instructions/states is pretty much the same for all x86 virtual machine monitors, including Xen. And if you simply run a LINPACK benchmark in VMware, you will notice that saying there is a lot of CPU overhead in VMware is definitively not true.
Also for the I/O, which is the place where Xen shines, you should be careful to put VMware and VirtualPC all together. While VirtualPC certainly attempts to emulate realistic hardware only. VMware, on the other hand, uses its own graphics and network adapter, and requiring users to use its drivers, at least to get the full performance. And for the disk I/O, both virtual machine monitors also show pretty different characteristics.
And you forgot the memory management, which has a big impact on guest machine performances.
I hate to be reduced to the “village idiot”, but wtf is xen?
I can unserstand the basics of “virtual machine” but in brief: what is the essence of xen? is it that I can run multiple instanceses of operating systems on one machine?
Sorry I missed the previous post…
Thanks Anonymous (IP: —.dyn.iinet.net.au)
I mean cheers mate!
I wonder how long it’ll be before we see the hosting industry dropping products like Virtuozzo for Xen ?
I’d expect them to phase Xen in on some new systems once they can put up a web-based management console. As of now, I don’t know of any hosting-friendly management console for Xen.
In the meantime, why replace what they have already paid for?
Hi all, I work on Xen, so the usual disclaimer: feel free to call me on anything if you think I’m being biased.
The problem with x86 is that there are some instructions which you need to trap in the VMM but which the CPU can’t trap for you. If you don’t find a way of trapping them then the guest will crash.
VMWare relies on scanning the kernel-level code and rewriting it at runtime in order to avoid this. It’s complex to do and has a performance cost – but it is very clever.
VMWare also needs to hide the underlying memory layout from the virtual machine, using “Shadow Page Tables”, which incurs some performance hit.
For benchmarks like LINPACK you shouldn’t find significant performance differences between any virtual machine systems (UML, Xen, VMWare, Virtual PC, QEmu + accelerator) – they should all be close to native. It’s stuff that’s OS intensive (lots of system calls and memory management stuff) or IO intensive stuff where Xen really shines compared to the others.
Thanks Mark. I appreciate your comments and insight.
Off hand, do you know of anyone doing a Xen-aware VM management console? I don’t know of any, though I would think that some folks would be keenly interested in this for Xen 3.0.
Because people neglect other VMware products like, ESX Server, GSX Server, and VMware ACE. VMware Workstation has much more of a performance hit than ESX.
For running multiple server instances you want to run ESX over the Workstation product.
Call me when it can run Windows2k/XP…. I run Ubuntu, and a couple months ago I was running off of Mandrake 10.1. Unfortunately, I still keep my system running dual boot with Windows2k — not because I still use windows for anything, but only to double-check the format of my OO.o documents in Office2k3 before sending them out to clients — and yes, I still find the conversion about 95% compatible.
I know I can run Office2k3 on Wine, but when I attempted to get Wine up and running approx. 1yr+ ago I had some difficulties, and gave up….maybe I should give it a go on Ubuntu – Ubuntu is my friend.
Running at 32bit though, which is the point.
Rumour has it that windows has been ported to it already as part of the research work. This rumour was fueled by the fact MS has a large lab in cambridge and works with them on a number of things (I don’t know if Xen is one of those things, though). However, Xen isn’t really designed for what you want to do – I’d think VMWare would be adequate for your needs.
I know I can run Office2k3 on Wine, but when I attempted to get Wine up and running approx. 1yr+ ago I had some difficulties, and gave up….maybe I should give it a go on Ubuntu – Ubuntu is my friend.
Yep, MS Office 2003 doesn’t work under Wine. Previous versions do, but not 2003.
Many other programs work quite a bit better under the current version of Wine vs. the one out last year at this time. For example, Picasa 2 ( http://picasa.google.com ) installs and runs well. (Not perfect — online help looks for an IE or Mozilla Windows HTML library and gives an error that it can’t be found — but very usable; photo editing works and indexing directories is not a hassle.)
The guys behind the XenoPhilia distribution (http://cosi.clarkson.edu/xen/) had developed a GUI control interface. Also, there’s the XenManager (http://xenmanager.dronestudios.com/cgi-bin/trac.cgi).
There’s also a web interface called “XenSV” that’s distributed with Xen – the guy who wrote that has come back and is hacking on a new version at the moment.
As well as managing multiple virtual machines, it’d be nice to integrate a deployment tool into the XenManager – in my spare time I’m doing some work to enable that. Then you’ll be able to effectively “apt-get” virtual machines onto your servers 🙂
Windows support will certainly happen (the developers recognise it’s a precondition to widespread adoption). It will require you to have a virtualisation-aware CPU (Intel are bringing their VT chips out Q2 this year, AMD next year). The Xen in FC4 (development version of Xen 3.0) supports running unmodified guests but not Windows (yet). I understand Windows now boots up to the splash screen on our dev boxes.
Of course, you could run QEmu or Win4Lin Pro in a Xen virtual machine under XenLinux right now, but it’ll be slow.
Xen gets benchmarked against an old copy of VMWare Workstation because later products by VMWare have a no benchmarking clause in their license. I’d expect that Xen is still much lower overhead than ESX server (depending on workload) but nobody can publish the numbers. This is unfortunate because ESX server would be a fairer comparison.
That said, you can’t get much better than Xen in terms of performance because it’s (measured) overhead is 0% on lots of benchmarks 🙂
Apart from binary compatibility, VMWare offer a comprehensive selection of management tools, which may put it ahead of Xen for some users. XenSource is developing enhanced management tools, although some of the higher level tools will be closed source.
Note also that VMWare will be supporting the virtualisation extensions from Intel and AMD, which will enable it to improve in performance.