Re: [Xen-users] gaming in a windows domU?

[Igor Chubin <igor@xxxxxxx>]

On Fr, Apr 13, 2007 at 11:53:05 +0200, Petersson, Mats wrote:
>  
> 
> > -----Original Message-----
> > From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
> > [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> > Igor Chubin
> > Sent: 13 April 2007 10:29
> > To: Andrew Yates
> > Cc: xen-users@xxxxxxxxxxxxxxxxxxx
> > Subject: Re: [Xen-users] gaming in a windows domU?
> > 
> > On Do, Apr 12, 2007 at 05:34:29 -0400, Andrew Yates wrote:
> > > I've been considering buying a second video and sound card, and then
> > > using PCI passthrough with a Windows domU for gaming.
> > > Has anyone tried this? I'm curious as to whether it's fast 
> > enough for
> > > recent games to be playable. The video card and CPU can 
> > handle gaming
> > > fine, but I'm not sure how much Xen would effect that. So has anyone
> > > done this? How well did it work?
> > > 
> > 
> > Do HVM domain support PCI passthrough?
> 
> No. But that's the EASY part to solve. The hard part is that the HVM OS
> isn't aware that what it thinks is a physical address is in fact not
> really the address that the memory controller is accessing when the
> software accesses a virtual address. 
> 

Mats, thank you for the answer.

As far as I know the problem will be eliminated
when as soon as IOMMU will be available.
Does IOMMU really solve the problem?

Question related to previous one:
HVM Windows Domains have poor IO-performance due to 
necessity of usage of qemu device model (and correspondent drivers).
Will the problem be eliminated (or alleviated at least)
with appearance of the IOMMU?


And question #3:
How is Intel virtualization technology [1] related with IOMMU?

[1] http://www.intel.com/technology/itj/2006/v10i3/2-io/1-abstract.htm


> If we simplify things[1] to make it easy to explain: Dom0 uses 0..256MB,
> HVM DomU uses 256..512MB, but thinks it got memory from 0..256MB. DomU
> tells the hardware that there is some data at 0x100000 (1MB), but we
> should really add 256MB to that address. So the hardware will use
> something that lives at 1MB in the Dom0 instead. Most likely, this will
> just lead to complete garbage being sent to the hardware, which isn't so
> bad. If it happens to be something that actually works with the hardware
> it may send your list of passwords to a random address on the internet
> or some such!
> 
> [1] In reality, each 4KB of guest memory could come from any 4K section
> of the machines memory, so it's not as simple as just adding an offset -
> but that's just a slight complication on top of the fact that DomU
> doesn't actually know that it's memory isn't where it thinks it is. 
> 
> --
> Mats
> > 
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> > 
> > -- 
> > WBR, i.m.chubin
> > 
> > 
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> > 
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> 
> 
> 
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-- 
WBR, i.m.chubin


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