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XFX 6870 CF not as good as single GPU

Ticklemehballlz

Ticklemehballlz

Ticklemehballlz

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Joined
15 Oct 2011
Posts
11
I really can't understand why this is happening, But in Battlefield 3 and Skyrim my 6870 CF setup isn't performing as well as one single card.

Windows 7 64-bit. PCI-E X16 / X4 (Overheats the second card if i use X8/X8 After much research it's not really a performance loss at all anyway using x4)

High settings.

Battlefield 3 6870 CF : ~40 FPS - ~60
Battlefield 3 6870 Single GPU : 60 FPS solid.

I want to be able to use the Ultra settings and get 60FPS and Two 6870's should be able to achieve this! but they are performing horribly.

I have Upgraded CCC Drivers from 11.10 to 11.11
and Downloaded 11.11 CAP 2

Then i tried Clean installing 11.11 and 11.11 CAP 2 and still no difference.

I tried over clocking the cards.

One thing i have not done is overclocked my CPU. I used to have it running at 4Ghz (AMD Phenom ii x4 955 @ 3.2) But i put it back to stock incase it made the pc unstable with CF. D'ya think i should put it to 4Ghz maybe it's bottle necking?

What's going on?
(Cannot buy a proper nice card. no money to do so. So if i should just sell the other 6870 do say so. but do not tell me to buy a 6970 or 6990 or a GTX 580. Cause i can't)
OR
Sell both cards for £100 each. and buy a GTX 560TI 2048MB From OCUK for £199.. that will be what i do if i can't sort this out.

Help Greatly appreciated!
 
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Overclock your cpu to 4ghz again as it could well be a bottleneck. Crossfire sli need a lot of cpu grunt to get the best from them. I also think 8x 8x would be better. You could try moving the bottom card to the top to see if that card better handles the heat. Running 4x at pci-e 2 speed is like running 8x at pci-e 1.
 
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I had this problem with a pair of of 5850's. I was told its because im running 8x/4x. So i brought a motherboard that's 8x/8x and it didn't work. So they said buy a better PSU and i brought a 850W XFX and still didn't work.
etc etc etc....

I aslo have the same CPU overclocked to 3.8ghz which did nothing either.

Here's my advice... **** crossfire!
 
I'm running 2*5850s also and getting no benefit in any of the games I play. Infact performance tends to be worse and crossfire has been disabled for 90% of the time. I second Mattuk69's last statement and won't consider a two card solution again.
 
Overclocked Phenom II X4 would pretty much guarantee to bottleneck crossfire 5850 and upward for any games that don't use all 4 cores fully.

While BF scale with with high number of cores, Skyrim only uses something like 2 cores if I'm not mistaken...so a Phenom II X4 955BE at stock would be a huge bottleneck...and assuming the crossfire 6870 delivering same frame rate as a single 6870, it would be not as smooth due to dual-GPU won't be as smooth as a single GPU on the same frame rate because of micro-shuttering, which tends to be quite noticable as soon as frame rate drop to below 30fps.
 
Also even in crossfire 6870's are still limited by 1gb of vram and battlefield 3 uses a lot more than that if you are playing at 1080p? It will cause a bottleneck on ultra settings which can cause stuttering and frame problems.

The 955 in skyrim is also a problem on highest settings because of the lack of cores being used. I was using a 955 clocked at 3.7 and a 6970. Was getting far from a great framerate. Have changed to an i5 2500k now and the difference is night and day.
 
Ticklemehballlz said:
I really can't understand why this is happening, But in Battlefield 3 and Skyrim my 6870 CF setup isn't performing as well as one single card.
Click to expand...
Have you tried physically switching the cards around? I've seen this with Crossfire before and it turned out the second card was faulty, something not evident until the monitor was connected to it.
 
I know not a "true" xfire card but my 4870x2 does not see any benefit on the second core. Infact no usage at all and if I enable the second core (through Catalyst AI) My frame rate drops massively. Get around 40-50 on the single core.

Again I know most of you are talking about true xfire and DX11 cards but through I would mention it is also a problem lower down the series. Driver 11.11 as well.
 
TheMorningStar said:
Isn't there an issue with bf3 and xfire?
Click to expand...

I have just gone from 2 5850's to 1 single 6950(unlocked to 6970).

I was OK with crossfire then BF3 started to crash with xfire so had to disable one. Crossfire is good when it's working. There are a few games that don't like crossfire.

Although lower framerate it still feels smooth.
 
Ticklemehballlz said:
D'ya think i should put it to 4Ghz maybe it's bottle necking?
Click to expand...

Definitely a scaling issue due to not enough grunt from the cpu, it's a waste not oc'ing that 555BE of yours to 4GHz, there should be a huge increase in scaling if you oc it imo.

BF3 is not cpu dependant, but scaling is cpu dependant, CrossFire and Sli need cpu grunt to scale properly.

Get Radeonpro:

http://www.radeonpro.info/en-US/Downloads/

and turn on the CrossFire usage bar and try out BF3 on stock speeds, then oc it back to 4GHz then see how much a difference there is.
 
TheMorningStar said:
Isn't there an issue with bf3 and xfire?
Click to expand...

No issues with crossfire here, runs ok but it does require a hefty cpu to get the most out of it!

Op, as others have said it is probably due to cpu bottleneck. Overclock and see if it helps, my rig in sig is cpu limited in BF3 (~70% scaling) though not to the extent that I actually get worse performance with crossfire enabled.
 
I had this exact same problem for about 9 months and it was doing my head in. I was running 2x 6970s on a Q6600. The crossfire performance was terrible when enabled in most games. I tried everything from drivers re-installs to OS re-installs. Turns out the problem was a bottlekneck with the CPU. Got a 2600K and now everything runs perfect with xfire. I'd honestly stop trying to fix it, it will just drive you insane. Try save up n get a better CPU and it will work.
 
Fens said:
No issues with crossfire here, runs ok but it does require a hefty cpu to get the most out of it!

Op, as others have said it is probably due to cpu bottleneck. Overclock and see if it helps, my rig in sig is cpu limited in BF3 (~70% scaling) though not to the extent that I actually get worse performance with crossfire enabled.
Click to expand...

Doubt it's bottleneck. It should at least give him the same he had with one card, no? A game won't slow down because of a bottleneck, it'll simply peak and not go any faster. I should know, I run SLI GTX 295 on a Core 2 Duo.


It could possibly be down to the 16x / 4x thing (because I personally haven't ever tried cards in that configuration) but it could also be what happens with Crossfire when there are problems.

IE - It's cack, get a single card.
 
Freddie1980 said:
The guy is running the two cards on x16 and x4 and complains of reduced performance.......your answer is there.
Click to expand...
Fraid not. I used to run my dual 6870s on a 16x/4x P67 board before switching to an 8x/8x Z68 one and performance in xfire mode didn't go up more than maybe 5% on average. (and this was with a 4.5GHz 2500K, so no CPU bottleneck to hold things back).
 
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