7950 Crossfire Problems

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mseagle2

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Apr 7, 2010
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So I just got 2 new 7950's today and I have been having problems with crossfire. Both cards work fine - I have tested each of them individually and they perform the same. I have tried using the 13.8 drivers and 13.4 drivers. Crossfire is enabled in CCC.

Ok so this is what happens:

during BF3 I only get around 30 FPS in crossfire (was getting 50-60 with single cards). In metro 2033 benchmarks tool I get the exact performance of a single card setup but both cards are active. MSI after burner shows GPU 1 only using 45% (and slowly works its way up to that) and GPU 2 instantly jumps to 100% (monitor is connected to GPU 1)

Any help would be great! Thanks!
 
Solution
06yfz450ridr


hmm thats really weird i would say do a complete uninstall of the...
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06yfz450ridr

06yfz450ridr

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Nov 28, 2012
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hmm thats really weird i would say do a complete uninstall of the drivers then disable your internet. now hit scan for changes in device manager and then run a install of the 13.6 beta drivers. I still cannot get my 7970 to not fail the driver update when trying to go to 13.8 no matter what i do and after catalyst would not install correctly and thats what fixed it for me.


those fps seem low for a 7950


also what powersupply do you have?

to me it seems like a driver issue but make sure to check you mobo manual to see what slots they say to use for xfire
 
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Solution
M

mseagle2

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Apr 7, 2010
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PSU is 750W corsair. Seems to be Ok. Mobo is a p8p67 and I am beginning to think this is the issue.

I did some more tests - I put 1 card in at a time. 1 test on bottom pcie, 1 test on top, repeat for second card. Both cards were getting the same FPS in benchmarks when on the top slot, but when in the bottom both would be 30-40% fewer FPS than their top pcie test. After reading a bit about my mobo it turns out to be a 4x pcie 2.0 on the bottom which is not enough bandwidth.

But would the 4x pcie account for a crossfire performance that is worse than a single card? Is this why 1 card goes to 100% usage, while the other never breaks 45% when in crossfire?

In the event a new mobo would fix this, which should I get? I have a i7 2600k and want to keep that so what 1155 socket mobo's seem to be the best these days? Also should I upgrade to a 850w psu or should I be ok with the 750w?

Thanks!

 
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06yfz450ridr

06yfz450ridr

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Nov 28, 2012
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hmm 750 should be ok but its pushing it. I know i have a 750 and im scared if i get another 7970 with my overclock it will be to much


from what you described does your board support sli bec that could be the issue as well but a 4x slot will limit your cards performance but you should still see anincrease in performance.

 
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M

mseagle2

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Apr 7, 2010
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I replaced my motherboard yesterday with a P8Z77-V LK and everything is working correctly. Crossfire is working great, and I did a pretty decent overclock on the cards and seems like the psu is holding up.
 
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iam2thecrowe

iam2thecrowe

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Jul 4, 2010
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"After reading a bit about my mobo it turns out to be a 4x pcie 2.0 on the bottom which is not enough bandwidth." < there's your problem, dont worry about your PSU, its fine. Although crossfire can technically be enabled with a 4 x slot, everyone i have seen try it has a problem, it introduces stuttering too, as the frame rendering time is different between the cards because of this bandwidth limitation. So, either sell the second card or both and get a better single card, or get a motherboard that supports 16x+16x pcie 2.0 for optimal performance.
 
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