SLI over multiple CPUs

[Ondaedj]

Hey, I've watched Linus for a long while now, never actually made an account here though until just a few minutes ago!

 

The reason I made an account is I have a question regarding SLI that I am having difficulties finding information on via the web.  Specifically I am interested in any potential difference, and how much difference, there might be when running 2 video cards in SLI on a dual CPU motherboard when each GPU is being handled by a seperate CPU vs a single CPU (assuming they are both running at x16 either way).

 

I suppose it is an odd question, but I figured if there was anywhere people might have an answer to this it would be here.  Can't seem to find any relevant information on this topic.  It is very well possible I am just searching for the information in a way that is not condusive to actually obtaining it though, so links to topics/information on this would be greatly appreciated!

[thekeemo]

It shouldnt make any diffrence

[Enderman]

First of all, the CPUs that can work in dual CPU motherboards are not good for gaming, so there is a performance decrease there.

Second, both CPUs are combined for processing power, they dont "handle" a GPU each

And finally, your GPU will perform the same no matter how many CPUs there are in your motherboard

[d3sl91]

It doesnt work that way, is the short answer. 

 

One program will use both CPUs as one (long story short...) and then use both GPUs as one (Again, long story short). Of course, there really isnt any minstream games that will use multiple CPUs like that, most still use 2 cores/threads. Some use 4. 

[Fgtfv567]

Just 2 GPUs? As long as you have 16 lanes, you'll be fine, running 8&8 will only make you lose one frame than if you run 16&16

[Ondaedj]

I apreciate all the fast responcces!  However I don't think I am being entierly clear. I fully understand the drawbacks and benefits of WS vs consumer grade processesors, and weather or not they are good for gaming seems like a completely seperate debate, although if you are ONLY gaming on a PC surely theres not really any reason to run xeons...

 

What I'm talking about here is on a board like this one: http://www.newegg.com/Product/Product.aspx?Item=N82E16813132268running on lanes 1 and 3 you would only be using the gen 3 link on CPU 0 but running on 3 and 5 you would be using both the CPU 0 and CPU 1 gen 3 link. If the answer is simply there is no difference then that's fine, but you are actually splitting the GPUs between 2 CPUs doing that so there has to be SOME comunication between the CPUs to compensate for that split right?

[J_DeMan]

It still works however, if the graphics cards are on PCI lanes of separate processors the processors must exchange the data for the GPUs. This is slower than just running the two cards in 8x PCI on the same processor's PCI lanes.

or if you want some more diagrams that are more in depth than mine: http://www.servethehome.com/answered-cpu-dual-processor-motherboard/

[Ondaedj]

:blink: 

 

lol, I thought I was about to get a yeah, it doesn't make any difference, but now you're saying there is a noteable hit to the performance..

 

Do you happen to know how much slower it would be, or have a link to some sort of benchmarks? The link you provided seems to be more about the disadvantages of not having the second CPU installed.

[KemoKa]

:blink:

 

lol, I thought I was about to get a yeah, it doesn't make any difference, but now you're saying there is a noteable hit to the performance..

 

Do you happen to know how much slower it would be, or have a link to some sort of benchmarks? The link you provided seems to be more about the disadvantages of not having the second CPU installed.

Not many people do it, but someone's bound to have done at some point.

You'd probably get 2-3 fps drops max, but that's not the problem, what's going to be affected is your frame times. CPU communication latency along with SLI? ooh, watch those frame times fly!