Re: [Xen-users] gaming on multiple OS of the same machine?

[Peter Vandendriessche <peter.vandendriessche@xxxxxxxxx>]

Hi Casey,

Thanks a lot for the bunch of information. Some further questions on the PLX and the VGA passthrough though.

On Sun, May 13, 2012 at 8:42 PM, Casey DeLorme <cdelorme@xxxxxxxxx> wrote:



> I
>  checked every major manufacturers high end boards, searching for one 
> with the best features to price and was aiming for the most PCIe slots I
>  could get.  Pretty much Every single board with more than 3 PCIe (x16) 
> slots came with some form of PCI switch.  Most of these PCI switches 
> break IOMMU in one way or another.

Yes, indeed, all of the 4-GPU-motherboards I know, have 2 PCI-e x16 slots which split to 2 x8 each (so 4 x8 in total). Is this always a fatal problem? Is there any easy way to find out if it will be a problem (like from the lspci info)?

The PLX was an entirely different form of problem, it merges device "function" with device identifiers.  If you run "lspci" you get a list of your devices, they are identified by "bus:device.function".
[...]

Armed with this knowledge, here is where you may run into problems:

-  Finding a board with 4x PCIe x16 Slots not tied to a PCI Switch

So, do I understand correct that it will work if and only if there is 1 "bus" per PCI-e slot?

-  Sparing enough USB ports for all machines input devices

What do you mean by sparing here? On a different bus than the PCI-e slots for the GPUs?

-  Limited to around 3GB of RAM per HVM unless you buy 8GB RAM Chips

Neither seems a problem (3GB RAM per machine or 8GB RAM chips). The price of RAM is fairly linear in its size.

-  Will need a 6-core i7 to power all systems without potential resource conflicts

Okay. That rises the price a bit, but it'd still be well worth it.

-  Encountering bugs nobody else has when you reach that 3rd or 4th HVM

This would probably be the real problem, given that I'm new to Xen.

I have never run more than one GPU in my computers before, so I don't know if there is some special magic that happens when you have two or more that they suddenly get even hotter, but I have to imagine that not to be the case unless you're doing some serious overclocking.

Depends on their size. Most GPUs are 2 PCI-e slots high (and occupy two of those metal plates on the back) and hence plugging 4 of them in leaves no space inbetween them, which hinders their air intake. Hence the need for watercooling the GPUs in this case.

The ASRock Extreme4 Gen3 does have enough PCIe slots that I could connect three GPU's and still have space for a single-slot PCIe device, but I only have a 650W power supply, and have no need for more than one Windows instance.

... and it has a PLX chip. Right? Or is a PLX chip not a fatal problem?

Secondary pass through works great for gaming, shows the display after the machine boots without any problems, and takes literally no extra effort to setup on your part.

Primary passthrough requires custom ATI patching, and what exists may not work for all cards.

I began looking into Primary passthrough very recently, because I use my machine for more than just games and ran into a problem.  Software like CAD, Photoshop, and 3D Sculpting tools use OpenGL and only work with the primary GPU, which means they either don't run or run without GPU acceleration (slowly).

Hmm? I'm not following. Most games also use OpenGL, right? And why would OpenGL not support non-primary cards? I know that OpenCL can run on any number of GPUs, so it'd surprise me if OpenGL was different. Do you have any link where I can read more background on this?

 

A lot to take in, but I hope my answers help a bit.  If you have more questions I'll be happy to share what knowledge I can.

Certainly, they're of great help. Thanks a lot!

Best regards,
Peter

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