2 x 7950 Crossfire Performance

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undrt0w
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Re: 2 x 7950 Crossfire Performance

Post by undrt0w »

I get what you mean.

GPU-Z was showing that the slower one was running on x4 3.0 and the faster on x16 3.0. Cuz this is what the Mobo (Asrock z77 Pro4) has:

- 1 x PCI Express 3.0 x16 slot (PCIE2: x16 mode)
- 1 x PCI Express 2.0 x16 slot (PCIE3: x4 mode)
- 1 x PCI Express 2.0 x1 slot
- 3 x PCI slots
- Supports AMD Quad CrossFireX™ and CrossFireX™

Sooo...i don't suppose there is a way to manually set them both running at x8 3.0 ?? If not, then it means....new mobo?? :evil:

But basically, when I had them both running at 810Mhz clock speed, the second would be fully loaded while the first and faster would go around 50%. When I had them at 925Mhz, they both would run around 50%.

A friend will be getting a new comp for xmas. I was planning to give him my old PSU so I will offer my old Mobo as well. It will save me some bucks if i go for this one:

http://www.asrock.com/mb/Intel/Z77%20Ex ... ifications

It has 2 PCIE3 x16 although it says:
- 2 x PCI Express 3.0 x16 slots (PCIE1/PCIE3: single at x16 (PCIE1) / x8 (PCIE3) or dual at x8/x8 mode)
If i get it right, when inserting both cards they will run at x8/x8 not x16/x16 ??

I knew there was something fishy when that idiot in the shop told me he has no crossfire cables to test it, because the cable is in the mobo box. I know they come with the vga card but i wasn't 100% sure so I didn't argue....then I go home and see the bridge on the bottom of the box. I also realized yday that there were no cables in the box...that fraker had taken them out. Stupid cunt, son of a whore!!!
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TheYonderGod
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Re: 2 x 7950 Crossfire Performance

Post by TheYonderGod »

Hmmm, if the motherboard claims to support crossfire, then it should work.. I don't want to tell you to buy a new motherboard when I really don't know for sure if that is the problem, but most(if not all) slightly higher end motherboards do split the 16 lanes into 8x/8x for 2-way crossfire/sli

See if I look at my mobo (Asrock Z77 Extreme4) manual it says
2. In CrossFireXTM mode or SLITM mode, please install the PCI Express
x16 graphics cards on PCIE2 and PCIE3 slots. Therefore, both these
two slots will work at x8 bandwidth.

4. Only PCIE2 and PCIE3 slots support Gen 3 speed. To run the PCI
Express in Gen 3 speed, please install an Ivy Bridge CPU. If you
install a Sandy Bridge CPU, the PCI Express will run only at PCI
Express Gen 2 speed.
but yours says
2. In CrossFireXTM mode, please install the PCI Express x16 graphics
cards on PCIE2 and PCIE3 slots. Therefore, PCIE2 will work at x16
bandwidth, while PCIE3 works at x4 bandwidth.

4. Only PCIE2 slot supports Gen 3 speed. To run the PCI Express in
Gen 3 speed, please install an Ivy Bridge CPU. If you install a Sandy
Bridge CPU, the PCI Express will run only at PCI Express Gen 2
speed.
Soo apparently yours is actually running it at 2.0 x4, which I do not believe is enough bandwidth for a 7950... But I don't know why they would claim to support crossfire (even up to 4-way crossfire) if this is the case. Like I said I don't want to recommend you buy something when I'm not 100% sure, but maybe if you have a local store with a good return policy you could buy one to test it out and return it if it doesn't help. Or perhaps look for a good black friday deal since it's coming up very soon anyways.
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Re: 2 x 7950 Crossfire Performance

Post by Necromancer »

The total bandwidth is x16
In SLi/Cross its splitting to 2 x8. The aasumption in SLi is that its not bandwidth thats caps you, but proccessing power.
PCI-E 3.0 doesn't mean that GPUs reached the PCIE 2.0 limit. Its just that the technology is available.

They claim it supports Crossfire/SLi becaise it technically does.
They put every dumb feature they can. Didn't you notice the "Quite 3.0™ Fanless solution" for a quite motherboard? All motherboards use fanless heatsinks today, its really not something unique they need to brag about. Its total BS.
S.M.A.R.T BIOS™ , SLI/Crossfire ready. Powersave™ - saving power when idle technology is all pretty much BS .

And what cables do you need to test it? The crossfire bridge.is the only thing you need. And nothing related to the GPU comes with the MoBo. You should't ask or buy from people who don't understand sh*t. They only try to stuff you unneccessery things, or worse, things that doesn't sell (probably for a reason).

I'd think a x4 is capping your card, but that doesn't mean thats THE problem. But I don't have any experiance with dual cards so im no expert.
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Jokerle
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Re: 2 x 7950 Crossfire Performance

Post by Jokerle »

Running different cards is asking for troubles, although the driver get better every year. Still I would make sure both cards have the exact same specs.

Can you set the both lanes to PCIE2 via BIOS maybe?


I found this somewhere:
Quote:
Originally Posted by buggers View Post
How much of a performance hit will there be if you use crossfire in a PCIe x4 slot compared to x8?


~10 - 15% + Microstutter
Microstutter is (potentially) a general problem of SLI/Crossfire setups though.
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Re: 2 x 7950 Crossfire Performance

Post by undrt0w »

@Joker: Yeah, the cards are identical with the exception that one has better clock speed (925vs810) but you can lower that easily. I read about the slower performance but I though it wouldn't be noticeable.

@Necro: Yeah, he was talking about the bridge. They are jerks but damn they are cheap...plus they work nice when putting everything in the case (its the little things I appreciate :P)

@Yonder: Doing some more reading I find that actually people don't recommend using the Pro4 for Crossfire. Because of the things you said. So, you might be right. My friend agreed to get the old mobo...I am giving him the old PSU as well for free...its a great bargain for him, but I just can't get myself to ask him money for the PSU. So, I will grab the new one when he builds his PC.

Thx guys for the help.
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Re: 2 x 7950 Crossfire Performance

Post by undrt0w »

Update and dumb question to follow:

I purchased a new mobo that has 2 PCIE 3.0 x 16. So now crossfire works on both with x8/x8.
After a fresh install of windows and no fiddling with other software (trixx or afterburner) but only setting 20% power control to both cards, the fps I get are pretty decent even when recording.

So the setup now is:

1) i5 3750k
2) asus p8z77 v
3) sapphire 7950 x2
4) benq xl2411t
5) samsung t220

Another problem that occurred though (except the fact that the mobo has a CPO_OPT fan and when it doesn't see one it sends a warning the pisses me off) is that I have a second monitor that I used to plug in to my integrated GPU via the analog port. Now, the new mobo will disable iGPU the second it sees there is an external GPU connected. After digging around it seems that there is no way to allow both. After all, it seems not a big deal since my new GPU has multiple outputs and I decided I can plug the second monitor in one of those. The GPU has the following ports:
1 x Single-Link DVI-D
1 x Dual-Link DVI-I

The dumb question is, to which one I connect the main monitor (benq) and to which one I connect the second (samsung)

Now, I have the benq on the DVI-I and the samsung on the DVI-D. Is this the way to go or vice versa? Also, do I loose on performance by having both monitors on the gpu? Given the fact that I read single DVI-D provides up to 60Hz and my monitor is 144hz, I guess i should stick with how it is.
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Re: 2 x 7950 Crossfire Performance

Post by o1oo1 »

you answered your own question.
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Re: 2 x 7950 Crossfire Performance

Post by Necromancer »

you couldn't plug it any other way since your BenQ only supports dual-link DVI.
having 2 monitors does effect performance as the GPU has more to render, but it depends what you're running.
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undrt0w
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Re: 2 x 7950 Crossfire Performance

Post by undrt0w »

Thx! :thumbup:

Well, the idea is BF4 in one and Battlelog map + TS on the other.
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Re: 2 x 7950 Crossfire Performance

Post by zorplex »

I get some crazy frame drops/stuttering with crossfire enable so I've just disabled crossfire for the time being. Hopefully they'll get some better driver support or perhaps with Mantles release we'll see some better crossfire support. Given a little time, I'm sure the crossfire support for BF4 will improve like it has with most other games.
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