RE: [Xen-users] Xen to Desktop/Workstation questions

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

You can run Xen on any P6-processor, just that you will not get the HVM features, as that requires either an AMD SVM or Intel VT capable processor, and as previously been adviced, not all Intel 9xx are VT capable. Without HVM, you will not be able to run unmdified operating systems, so you need to have access to the source-code and suitable patch(es) to modify the source to understand Xen-isms. If you have a few millions of dollars, a safe room with secure access, and willing to sign your entire life away to Microsoft, you can get Windows source-code. It's not impossible, but it's pretty close to... The next question is getting a patch put together by someone who understands this...

 

I do know from experience (of moving a hard-disk from one machine to another) that Windows copes poorly with hardware changes. How poorly depends on which version of Windows and which particular changes you make to the system, the smaller the change is, the more likely it is to work well - and also if the change is needed "early" in boot, it's harder to cope, because the infrastructure to test PnP features may not be available, and a driver will possibly be loaded "blind", i.e. the driver is loaded without checking if the hardware supports it or not. Depending on how well-written the driver is, it may work well, or not so well...

 

I believe, but I'm not 100% sure (as I didn't write the documentation) that the AGP/DRM support is related to Xen running Para-virtualized (aka PV guest, i.e. modified source-code) guests. Which works fine, but doesn't support Windows, which is what your next question related to, so I presume that you actually wanted these features to work in Windws. Since this is not a PV guest, it will require full-virtualization.

 

I've written abou this several times, and if you do a search you'll find some good explanations, but in short: We tell the OS that it's got memory from 0..256MB, but that's not actually where the system gets loaded, in physical memory. For arguments sake, we say that Windows is loaded at 256MB..512MB. Now, some application wants to draw something to the screen, and it's a bimap located at 90MB into the guests memory. Windows, knowing that memory starts at 0, will say to the graphics card that it should draw the bitmap at 90MB. However, that memory is NOT owned by the guest, but belongs to some other guest, and 99.999% sure to NOT contain a bitmap, or anything else useful for the graphics card. So it's not going to work, however much you'd like it to.

 

The most likely working system you could get, if you actually want high-performance graphics on Windows would be to get the a virtualization system that starts off in Windows, and thus you can use the graphics hardware in Windows, and other operating systems get virtualized on top of this windows installation. It's unlikely that both the game(s) and virtual machines will run well at the same time, but at least you can possibly get them to run simultaneously, and you can certainly get Windows to run games without having to resort to two different installations.

 

In the future, there will be hardware to support remapping the physical memory accesses that Windows (and other operating systems) tell to hardware, such that we can "adjust" the REAL memory address that (for example) a graphics card performs it's operations on. But it's not available today. This hardware is called IOMMU.

 

--

Mats

---

From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Alexandre Miguel Pedro Gomes
Sent: 03 July 2006 17:11
Cc: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Xen to Desktop/Workstation questions

I only had read this part, and misunderstud the next few lines:

"Xen currently runs on the x86 architecture, requiring a ``P6'' or newer processor (e.g. Pentium Pro, Celeron, Pentium II, Pentium III, Pentium IV, Xeon, AMD Athlon, AMD Duron). Multiprocessor machines are supported, and there is support for HyperThreading (SMT). In addition, ports to IA64 and Power architectures are in progress." - Xen Manual

I believe Windows had, and still has, something called Hardware Profiles, couldn't that be used to smooth this "hardware" changes?

Related to 3D, Xen Manual "What's New" says "AGP/DRM graphics" but I couldn't find any other reference to either AGP or DRM in the Manual - isn't this supposed to enable some acceleration? I would not be bothered if I only could get 3D acceleration at one OS (Windows).

At last, is there any Virtualization product either free or commercial that can provide me all this?

On 7/3/06, Petersson, Mats < Mats.Petersson@xxxxxxx> wrote:

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of
> Jerry Amundson
> Sent: 03 July 2006 16:35
> To: xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-users] Xen to Desktop/Workstation questions
>
> On Sun July 2 2006 21:09, Alexandre Miguel Pedro Gomes wrote:
> > Hello,
> >
> > I'm buying a new computer with a Pentium D 9xx processor and I was
> > thinking of using Xen to run Linux and Windows XP Pro. The first
> > thing I noticed in the Xen Manual is that Pentium D isn't
> listed as a
> > supported processor, only x86 is support and not 64Bits. Can I still
> > run Xen?
>
> Probably. Depends on your "xx" - see
> http://wiki.xensource.com/xenwiki/HVM_Compatible_Processors
> The manual lists "x86/64" - did you mean something else?
>
> > Related to graphics support I whish to know how do we "switch" guest
> > OS if only one monitor is availble? If I've a graphics card with 2
> > outputs (dual head), or a SLI configuration, is it possible to use
> > dual head in the guests? And to have one OS in one monitor and the
> > other in the second monitor? If I've two guests, Fedora and Windows
> > XP Pro, can I run 3D accelerated games in Windows?
>
> Can't help there - you might look for recent thread
> on "devices", "graphical", etc.

Simple answer is NO, you can't run 3D accellerated anything under Xen,
because the way that graphics cards (except really REALLY old ones) work
means that driver needs to know the actual physical address in memory,
which is "lied" about to the OS in HVM guests...
>
> > Can I "tri"-boot one of the OSes, that is, run a guest
> under Xen then
> > reboot and run that same OS without Xen?
>
> Probably. (sorry - ask a general question, get a general answer ;-)

As Jerry said, probably: As long as the OS lives in a partition rather
than a file, yes, it would be possible... But some PnP-OS's get a bit[1]
confused when the modern IDE controller suddenly gets replaced with a
pretty basic old-style one (QEMU IDE) after reboot, at may not even work
correctly under those circumstances... Same with graphics cards that
appear/disappear depending on which way you boot the system, not always
handled OK [although since the graphics card isn't immediately needed
for the actual boot, more likely to work].

[1] Some OS's go a bit beyond "a bit" on the confused scale, more like
completely and outright confounded under these circumstances... Win98
does not like having the main chipset replaced under it's feet, for
example - it just plain stops working if the new chipset isn't nearly
identical to the old one - unless you set some particular value in the
registry just before shutting down to say "Please use basic components,
I've just changed everything - rescan PnP components on boot", which is
slow and easy to forget... ;-)

--
Mats
>
> jerry
>
> _______________________________________________
> Xen-users mailing list
> Xen-users@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-users
>
>



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--
Alexandre Gomes, Portugal

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