Why only 4-way CF/Quad SLI?

[Lepton87]

Why both NV and AMD only supports four GPUs working together? Are there any technical limitations with AFR and more GPUs or is it dictated by financials i.e. why spend resources for an extremely small niche of the market?

 

[JAG87]

AFR doesn't scale well at all past 3 GPUs. There once was split frame rendering which with some games scaled almost linearly with more GPUs (I remember FEAR being one of these game), but SFR generally sucked with 90% of games, so AFR was preferred going forward.

 

[Lepton87]

It does scale, I get about 20-25% more fps with 4 gpus instead of 3 in the benchmarks or games that actually use all of my cards. It's far from the theoretical 33% improvement but still noticeable. 8 gpus could work in pairs on 4 frames with both AFR and split screen rendering, but I guess it's way to much to ask from driver teams.

 

[AdamK47]

I'd get another GTX 690 for 6-way if I could.

 

[Final8ty]

For games 4 GPUS is the windos-OS max but for other work you can have more.

 

[lavaheadache]

I'd get another GTX 690 for 6-way if I could.

I can't imagine that you would get any extra tangible performance from another 690.


Actually you can, Get one as a dedicated physx card. I bet people wil openly hate you for it.

 

[Lepton87]

For games 4 GPUS is the windos-OS max but for other work you can have more.

Are you saying it's a windows limitation not driver limitation? We all know that for compute CF or SLI isn't needed.

Actually you can, Get one as a dedicated physx card. I bet people wil openly hate you for it.

Why? Because they think psyx isn't worth it? If he really enjoys psyx and psyx games that much I see nothing wrong with that. Personally I only played one game that supported psyx and so far didn't like it. (BL2) I thought it would play similarly to FO3 and FO3:NV which I enjoyed very much, but it doesn't. The only reconciliation is that it scales really well with 4 cards, but that game is not very demanding and I get 160fps which is excessive if someone isn't using 3D, but as far as I know you can't get 3d along with 2560 resolution and IPS panel.

 

[Final8ty]

Are you saying it's a windows limitation not driver limitation? We all know that for compute CF or SLI isn't needed.

Why? Because they think psyx isn't worth it? If he really enjoys psyx and psyx games that much I see nothing wrong with that. Personally I only played one game that supported psyx and so far didn't like it. (BL2) I thought it would play similarly to FO3 and FO3:NV which I enjoyed very much, but it doesn't. The only reconciliation is that it scales really well with 4 cards, but that game is not very demanding and I get 160fps which is excessive if someone isn't using 3D, but as far as I know you can't get 3d along with 2560 resolution and IPS panel.

Its windows limitation, max 4 GPUS games.
8 GPUS for other tasks.

 

[WiseUp216]

I'd get another GTX 690 for 6-way if I could.

Do you have a link to a picture of your build? Those specs are a thing of beauty.

 

[N4g4rok]

Do you have a link to a picture of your build? Those specs are a thing of beauty.

Curious as to the value of all those parts as well.

 

[jackstar7]

Isn't there a limit to PCIe lanes/bandwidth that would cause issues at some point?

 

[Wall Street]

I think it may have something to do with the connections between the cards and PCIe. With one GPU, you need one one connection between the CPU and the GPU. With two GPUs, you need two connections from the CPU, one to each GPU, and a connection between each GPU for a total of three connections. 4-way SLI requires 15 total possible connections. For six way SLI with cross links between each GPU, you would need to connect seven devices (6 GPUs and a CPU) which can each talk to all of the other devices for a total 28 possible connections.

Having each device share 1/28th the bandwidth would be a problem.

 

[Black Octagon]

Because motherboards are too small to allow 6 cards while keeping other peripheral slots free?

 

[AdamK47]

I cannot post pictures or discuss my PC in any manner on these forums. The haters would descend upon me in no time.

 

[WiseUp216]

I cannot post pictures or discuss my PC in any manner on these forums. The haters would descend upon me in no time.

So why the signature?

 

[AdamK47]

So why the signature?

I've always had one with my current PC specs. The fact that we're talking about it now alludes to the before mentioned problem.

 

[WiseUp216]

I've always had one with my current PC specs. The fact that we're talking about it now alludes to the before mentioned problem.

I was just curious. No need to get all weird about it.

 

[boxleitnerb]

Btw input lag increases with each additional GPU. I hear with 4 GPUs it is already pretty bad.

 

[PowerK]

Btw input lag increases with each additional GPU. I hear with 4 GPUs it is already pretty bad.

Here is some interesting info from Nvidia on this.
http://developer.download.nvidia.com/whitepapers/2011/SLI_Best_Practices_2011_Feb.pdf

One additional detail worth noting is that while input latency is the same on SLI AFR configurations as it is on single GPU configurations (each frame will take as long to be complete), inter-frame latency is reduced due to parallelism, so the application appears more responsive. For example, if a typical frame takes 30 ms to render, in a 2-GPU AFR configuration with perfect scaling the latency between those frames is only 15 ms. Thus, increasing the number of frames buffered in SLI does not increase input lag.

 

[boxleitnerb]

Interesting, I thought it was different. Yet they compare different fps. Of course more fps will reduce input lag.
How about 60fps@single GPU vs 60fps@4-way SLI/CF? Any practical observations from AdamK47 or anyone else with 3+ GPUs?

 

[moonbogg]

1st world problem #1.

 

[PowerK]

Interesting, I thought it was different. Yet they compare different fps. Of course more fps will reduce input lag.
How about 60fps@single GPU vs 60fps@4-way SLI/CF? Any practical observations from AdamK47 or anyone else with 3+ GPUs?

I've been using GTX 690 Quad-SLI since May last year, and frankly speaking, I have not noticed any input lag (only increased fps). However, I play games for fun so people who play competitively may find different results.

 

[FalseChristian]

Don't you people think that Quad SLI/xFire is overkill anyway. The sweet spot is 2 GPUs in SLI/xFire. Anything after that is just a waste of hard-earned money.

 

[Final8ty]

Don't you people think that Quad SLI/xFire is overkill anyway. The sweet spot is 2 GPUs in SLI/xFire. Anything after that is just a waste of hard-earned money.

The sweet spot is 3 and it always has been.

 

[FiLeZz]

3 for the win