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3-way sli slower than 2

About the clocks of the card, can you review this when they are under load, with a heaven benchmark window for example. When the card is then under full load and you open the view with all vitals you can see how much load the cards do have and how much of the power target. Those information will help to see what is causing the issue.
 
I will try that and report but to reiterate; with the settings as "use 3 monitors, no sli" my windows desktop is fast. As soon as I turn on sli, dragging windows is slow and sticky. These two modes can be selected from the nvidia control panel without hardware changes or rebooting. I really don't think this issue is with loading.
Plus, with two cards installed and 2-way sli enabled I had no problems. It's only with 3-way sli I see these issues.
Once I get a useable windows desktop back I will worry about benchmarking!

BTW is there a correct way up for the sli bridge to go? It appears to fit either way so I installed it with the text in the normal orientation.

Cheers;
Jeremy
 
jrichemont said:
BTW I only have low power ssd drives in this system so there's a bit more headroom for the PSU. I used this psu calculator for my setup and it suggested 927w. I'm not taking that as iron clad but even if it's out a bit I should have at least 150w to spare.
Click to expand...

Agreed.

Corsair AX1200i Psu benching Heaven 4
Sli 780ti
4770k @4.4ghz
8X 140mm fans
2x HD
2X SSD

Highest was 624 watts add another 780ti only around 900 watts, unless this Psu is just more efficient

 
How do you plug the 3 screens to the 3 way SLi setup ?

3-Way SLI 2D Surround Gaming
GTX680-ConnectorDiagram-3WaySLI-2DSurround-RecommendedOption.png

http://www.geforce.com/whats-new/guides/how-to-correctly-configure-geforce-gtx-680-surround#4
 
As shown. I think the green DVI sockets are DVI-D and those are what I use. I have played around with other configs but none work properly or won't allow sli. For the 2-way I used both DVI sockets from the top card plus the first DVI from the second.
 
OK. The new drivers are just the same, all 3 boards report they are running at 324Mhz and around 45C when just running windows desktop. Dragging windows around has all the feel of a raspberry pi. Forgiveable if you are using one of course but I really feel I should be getting better from my setup.
I ran gpu-z and it says I get 16x, 8x 8x as expected. Running the little benchmark shows 1200Mhz gpu speed and around 60C temps.
This rig should fly but it ain't. Any more ideas gratefully received!

Jeremy
 
One other thing I notice; the middle card stays around 50C while running the valley benchmark. I get < 20 FPS on that but cards 1 & 3 run @80C whereas card 2 runs @50C. This is odd.
 
I'm starting to suspect a faulty card.

Try to run 2 way SLi with the one that only gets 50*c hot when running valley benchmark.
 
I'll try. I am assuming the order shown in the valley benchmark matches the physical order? So the middle one with low temps is actually the middle card?
 
Ok. I have decided to accept that 3 cards in sli mode are unusable for windows. I did some timings and got 40FPS for combos of two cards and 50FPS for all three. Windows works find for two but crap for three so I will keep the settings on 'all monitors' until I want to play a game then I change to 'sli three way'.
It is very far from ideal but I can live with it..

Thanks for all you suggestions etc

Jeremy
 
I still think your CPU is a massive bottleneck for 3 780s.

If you agree with my estimate that your 4 core performance @ 4.5Ghz is roughly the same as my 2600k @ 3.4Ghz. (the rare games that can use 6 cores and/or Hyper-Threading may fair better)

With my sli 670s I generally get a 15-20% improvement going from 3.4 Ghz to 4.5 Ghz. (Wow gets 25-30%)

So safe to assume at stock I have at least a 15% bottleneck. The 780s look around 25-30% faster than a 670. So you already have a big bottleneck. Then you add a third card. :>

Now the desktop problems suggest there is something else at play, but still as far as I can see you have a massive bottleneck. :/
 
An update on this; I get 50fps with the 3 cards in sli and 40fps with two (heaven benchmark, everything maxed, 5760x1090). Windows performance with 3 way sli sucks but its easy enough to change mode to 3 monitors no sli and performance on the desktop goes through the roof. So, it remains a mystery but I spend most of my life dragging windows around. The occasions when I want the 3 monitor sli gaming experience I will just have to change modes.
Thanks for everyone's advice and do post if you get a brainwave …
 
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