PCI-E x8 5870 Crossfire Bottleneck?

Derfman

[H]ard|Gawd
Joined
Jan 12, 2007
Messages
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Hey [H].

I have spent the past hour and a half googling to my hearts content, but I can not get a straight answer on this question. All the answers I have seen related to the 4000 series of graphic cards and unless the PCI-E bandwidth needs of the 5000 are near the same then I haven't found an answer to my question.

I want to add a second 5870 card for Crossfire, but doing so would put all my true x16 slots at x8 and I am afraid that this will be more of a bottleneck in crossfire then it would be worth it performance upgrade wise.

Currently I am circumventing the x8 issue on my 5870 by the organization of my cards. With my motherboard, the top and 3rd x16 slots run at x16 as long as the second or fourth x16 slots do not have any cards in them.

So my 5870 is in my third slot running at x16 while my 9800 GT (for Physx) and my SAS controller card are in the first and second slots with only x8 available to them.

For reference:

This is my motherboard: NewEgg Link Gigabyte GA-X58A-UD5.

This is a picture of my current setup:

DSCN0399.jpg


In order from top to bottom:

First Slot: 9800 GT (Physx)
Second Slot: SAS Controller Card (it is a x4 card)
Third Slot: Radeon 5870
Fourth Slot: Open

Basically if the bottleneck is as low as single % numbers then I will still need to find a solution to the need for extra space, but right now I am trying to see if it is even worth going through all that trouble at this point.

Thanks in advance for any advice given.
 
I was thinking about making a similar choice; 1 5850 to 2 5850's. Doing so would knock both slots down to 8x 2.0. I suppose I could manually lower the lane width to 8x with my single card and see if I take a performance hit...
 
I was thinking about making a similar choice; 1 5850 to 2 5850's. Doing so would knock both slots down to 8x 2.0. I suppose I could manually lower the lane width to 8x with my single card and see if I take a performance hit...

That's what the one review I read did, but supposedly there is more bandwidth overhead when using Crossfire and that is why I still am looking for this answer. :)
 
First things first, what resolution are you gaming at?

Regardless, I'm pretty sure that it won't be bottlenecked at 8x on 2.0. Everything that I've read or seen indicates that we really haven't encountered bottlenecking on 8x width except for maybe dual gpu cards in quad sli/CF
 
First things first, what resolution are you gaming at?

Regardless, I'm pretty sure that it won't be bottlenecked at 8x on 2.0. Everything that I've read or seen indicates that we really haven't encountered bottlenecking on 8x width except for maybe dual gpu cards in quad sli/CF

Your most likely right. I game at 1920x1080.

I think TechPowerUp looked at this and found you weren't bottlenecked until you hit x4.

That was one of the articles that I had read but it didn't cover the card being in Crossfire.
 
This is the review you want to see. They tested 5870 CrossFire on P55 8x8 versus X58 16x16:

http://www.tomshardware.com/reviews/p55-pci-express-scaling,2517-10.html

Note that this board does not have an NF200 chip on-board, just straight 8x8. See here for the comparison with NF200:

http://www.tomshardware.com/reviews/p55-crossfire-nf200,2537-9.html

End result: you lose about %5 performance going with 8x8 over 16x16 for dual 5870s; no biggie. Don't attempt triple CrossFire on P55 without the NF200 bridge (but that should be obvious).
 
I have the EVGA Classified board(with the NF200 chip).
For cooling, I have my 5870s in the top PCI-e slot (x16) and the third PCI-e slot (x16/x8).

I've never gotten a straight answer from anybody, but due to my configuration, I would guess I have one card running at x16 and one card at x8.

I have seen no performance hit from this setup. I could game at 1920 x 1200 all day long in DX10 or 11 pretty much at maximum.

Now with my EyeFinity(3 x 24" monitors), the system is struggling in full DX11 but that's not too unexpected. I can run any other game at full tilt in EF however. I've had to dial down DX11 AvP to get it to run smoothly.
 
in 3dmark vantage performance at X16 2.0 i get 16339 single card at X8 2.0 same card I get 16289 the difference is minimal and only noticable in 3dmark vantage and maybe 3d06, games you will never see a difference. current gen cards do not use up full 2.0 bandwidth hence the reason nobody is pushing pci-e 3.0 out the door. if it were pci-e 1.0 that would be a different story
 
Awesome! Wonderful replies guys! Now I just need to make sure I don't dive into my savings account for this and a larger case. :)

I have seen no performance hit from this setup. I could game at 1920 x 1200 all day long in DX10 or 11 pretty much at maximum.

Now with my EyeFinity(3 x 24" monitors), the system is struggling in full DX11 but that's not too unexpected. I can run any other game at full tilt in EF however. I've had to dial down DX11 AvP to get it to run smoothly.

EyeFinity is probably the last thing I need in my setup, if you think my PC case is cramped you should see the room I have all this stuff in.

I'm glad to see that one more 5870 will probably place me in the "it feels good man" category for at least another year. Though I can't help but find more reason logical or not to burn a bigger hole in my pocket.
 
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