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Tek20
1st Nov 2009, 23:00
I have two 8800GT's in SLI. However, when I disable SLI I get the same performance as I do with SLI enabled. Correct me if I am wrong, but if I disable SLI then it automatically dedicates a card to PhysX? I am running the newest drivers. PhysX is set to Normal, AA off, Detail Level: Very High. Resolution: 1440x900.

Bench with SLI Disabled:
Min: 33fps
Max: 60fps
Avg: 54


Bench with SLI enabled:
Min: 32
Max: 60
Avg. 54



I just disable SLI in the nVidia control panel and enable PhysX to dedicate a card correct?



Here are my specs. Thanks.



Asus P5ND nForce 750i SLI, Socket 775, PCIE,DDR2
Intel Core 2 Quad processor Q9450, quad 2.66GHz cores, 12MB L2 Cache
DDR2 Memory 4096MB Corsair XMS2 DDR2800
2 x 512MB EVGA GeForce 8800GT DDR3 in SLI, PCIE,Dual DVI/HDCP
Integrated High Definition 7.1 Channel Sound
750GB Hitachi 7200rpm 16MB Cache SATA 300 w/NCQ
Windows Vista Ulimate 64-bit

deders
1st Nov 2009, 23:51
Yep, that's all I had to do. What happens when you put Physx on high?
Also just to be sure what do the SLI and Physx visual indicators say?

Tek20
2nd Nov 2009, 00:16
The indicators say PhysX > GPU and SLI. The green bar of the SLI indicator stays centered and does not move. When I shut SLI off the PhysX indicator still says Physx > GPU.


I set PhysX to HIGH and ran two benchmarks:

SLI ENABLED w/ PhysX High - #1
Min: 1
Max: 61
Avg: 48


SLI ENABLED w/ PhysX High - #2
Min: 2
Max: 60
Avg: 38


===========


SLI <DISABLED> w/ PhysX High - #1
Min: 14
Max: 60
Avg: 53


SLI <DISABLED> w/ PhysX High - #2
Min: 18
Max: 71
Avg: 52




Now there is a difference with PhysX on High between SLI and SLI disabled. Would that mean that with PhysX set to normal the two 8800GT are not hitting their limit in SLI Mode or in Dedicated PhysX card mode?

Tek20
4th Nov 2009, 16:08
Any ideas on this?

deders
4th Nov 2009, 16:20
It probably means that your card isn't being stressed by physx on the normal setting.

Also, if the game detects that you don't have enough physical shader cores available for physx calculations, it will stop some of the effects, sometimes in mid air (paper/leaves etc) and sometimes flying bricks will just disappear.

This is most likely to happen when you are playing in SLI, because each card has to render the scene in alternate frames. When you disable SLI then there is an entire cards worth of shader cores available so it can calculate more effects without dropping others.

I wouldn't take too much notice of the max and min frames in these benchmarks either. When I've benchmarked my system, there wasn't any point that I noticed that my framerate actually went anywhere near the values it reported at the end. especially considering for some of them my framerate was limited to 60fps via vsync and I was getting over triple that after some run-throughs, even though fraps clearly didn't go above 60. The average is probably the most accurate.