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