R6950 Crossfire issues

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KingOtaku

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Now, I just began to crossfire my Radeon 6950's. In some games, it works (most notably Metro 2033) but in others it fails completely. In BD2, I lose about 10-20 fps. And worst of all is that in BF3, the game that I specifically got a second card for, crossfire adds absolutely no FPS gain. I just want to know if anyone else has been having crossfire/driver problems in this game.
 
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cdub1980

cdub1980

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6950's have shown 75-85% scaling when used in CrossFire, so I'm surprised with the results. BF3 has shown to have especially good scaling when using CrossFire. Make sure you have the latest drivers, AMD released a preview driver for BF3 that you can download...

http://support.amd.com/us/kbarticles/Pages/GPU124AMDCat1110PreDriverV3.aspx

Also, if you installed the latest Catalyst Application Profile (CAP) for BF3, you need to uninstall your AMD drivers and just reinstall the above linked drivers. AMD noticed that the CAP for BF3 wasn't working as intended and was causing problems. You can review this article where they initially had major issues using CrossFire in BF3, but then did what I just recommended and it worked flawlessly...

http://www.hardocp.com/article/2011/10/25/battlefield_3_preview_performance

Other things you might want to mention...what are the specs on your computer? what are the PCIe lane speeds on your motherboard? Those might help others recommend solutions.
 
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KingOtaku

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Yes, I enabled crossfire in CCC...
And about the CPU; yes, I know, it's not the fastest CPU, but I was under the impression that it wouldn't affect FPS much, and even if it did, it shouldn't completely negate the effects of Crossfire...
Remember; Crossfire works in Metro, and I have definitely been getting better results in benchmarks(FurMark, Unigine, etc.) But there is no effect in BF3, which is why I think it is drivers.
I'll check the bios, and see if it isn't already set to dual 8x
 
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bystander

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Often, when a CPU holds performance back, it creates a bottleneck to the point that no matter how much graphical horsepower you add, it will not improve FPS. When people say that your CPU shouldn't hold FPS back much, they are referring to typical single GPU systems. If you want a dual GPU system, you need a lot more CPU power, or a much higher resolution (higher resolutions mostly only add work for the GPU, not the CPU).

What is your resolution, and what FPS are you seeing?
 
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KingOtaku

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I am seeing around 50-70 fps at 1600x900. I know the resolution is low for a dual GPU system, but I plan to upgrade next time I have the money...
But, would my CPU really hold me back that much? And, if it does, than how come I'm getting such a good FPS (45-70) on Metro 2033?
 
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bystander

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If you are bottlenecked by the CPU, then the FPS you are seeing will never be higher under any condition, but going to a higher resolution may not lower your FPS any.

Every game is different. Some put a lot more stress on the CPU, and others put more stress on the GPU. At your resolution and GPU setup, you'll almost never run into a case where your GPU's hold you back, but you almost always be limited by your CPU and refresh rate when it comes to actual displayed FPS.

Metro 2033 is likely a game which has lots of GPU intensive work, and not as much CPU work. Other games, may stress the CPU more. For most people Metro 2033 gets low FPS due to their GPU, and since you have way more graphics power than your resolution needs, you get high FPS.

EDIT: to help illustrate what is going on, let me try to explain it with a metaphor.

When a frame is rendered, there are several things that are taking place at once. The CPU is usually responsible for tracking physics and where things are located, as well as running logic. The GPU assists by drawing the textures, creating wire frames with tessellation, doing lighting effects and so on. They perform different tasks.

This is a bit like building a car. There is an assembly line. Imagine there are two phases to building a card. Building the engine, and building the body. If the assembly line can build the engine in 8 hours, and a 2nd assembly line builds the body in 4 hours, how long does it take to build a car? 8 hours, because no matter how fast the engine is built, you still have to wait for the body to be built.

The same thing often happens with a computer. If the CPU can only do all of it's calculations fast enough to display 40 FPS, and your GPU can handle up to 200 FPS, how many FPS will you get? 40 FPS.
 
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bystander

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One more thing that you should be aware of. If you have a typical HD monitor/TV, you likely are running at 60hz. With a 60hz limitation, the maximum displayed FPS you will ever see, is 60. Going to 200 FPS, will still result in only 60 frames being displayed. With a 120hz monitor, that limit is raised to 120 FPS.

If the lowest FPS you are getting is 45, you don't have any real troubles.
 
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KingOtaku

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Hmm....but I still don't think my CPU would bottleneck it that much; I have a friend playing on the same system (except he has a single 6970 and at 1080p) and he consistently pulls 70+, even on very heavy scenes.
Edit: Yes, I know that, but I still would like to know why I'm not getting an FPS gain. Even if it doesn't make a difference, I want to know my card is working.
 
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bystander

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What's his CPU? If he has a Sandy bridge system, his CPU is likely much faster than yours.
 
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KingOtaku

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All high, Post-processing anti aliasing (FXAA) all the way up, no MLAA.
The bus interface is PCI-E 2.0 8X
I know the cards can handle PCI-E 2.0 16X, but I don't think that would be the problem, but what do I know?
 
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thrakazog

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I am currently running 2 x 6950's in X-fire, and get amazing results in BF3 on ultra settings.

I chose not to use the "preview" ( beta ) drivers, and instead opted to stay with the 11.9 release drivers and the 11.9 cap 3 ( CAP 4 released today ) X-fire app profile. I can't promise it will fix your problems, but has had flawless operation for me in BF3.

- 11.9 release driver

http://support.amd.com/us/gpudownload/Pages/index.aspx

- 11.9 cap 4 application profile

http://sites.amd.com/us/game/downloads/Pages/crossfirex-app-profiles.aspx
 
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bystander

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Just a note, if it hasn't been mentioned yet. If you are indeed bottlenecked by the CPU, even with 1 GPU, adding a 2nd will decrease performance, has the overhead to run 2 GPU's steals more CPU power.

When you have a single GPU enabled, does your performance look closer to your friends?

That said, make sure you have the latest CAP drivers as you mentioned as well. BF3 was just released, so it's going to require the latest drivers and profiles.
 
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ilysaml

ilysaml

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and that called excess of GPU power
 
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ilysaml

ilysaml

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But that's when V.Synch is enabled, right ? and even if the GPU is rendering more than 60 FPS the eye doesn't take a benefit from this.
 
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bystander

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No, it's always limited to 60 displayed FPS. Granted, your video card might generate 200 frames, but the frame buffer, the images are written to, is only written to the screen at the rate of your monitors refresh rate, which is 60hz on most monitors.

V-sync just prevents the video card from writing to the frame buffer except when it's in vertical retrace mode (the period that it is not updating the screen) to prevent the possibility that the video card is writing to it at the same time, resulting in a melding of 2 frames, otherwise known as screen tearing.

And the eye takes the benefit of much higher than 60 FPS, but your hardware just does not display more than 60 FPS without higher refresh rate.

Read this: http://www.100fps.com/how_many_frames_can_humans_see.htm
 
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gnomio

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Here's another thing. LCDs don't have a refresh rate. They don't have a electron gun like a CRT do. The hz you see in windows is a emulation because the need to receive the images the same way as a CRT did.
Fps is what your gpu produce. You can get 120fps on a 60hz monitor. Your pc won't slow down or nothing youll just see tearing and ghosting issues because the gpu and the LCD went out of sync. 70 fps on a 60hz is fine. The more it goes out of sync the more ghosting and tearing will appear.
That's why they say buy a gpu to power your monitor not your ego. Then youll be able to eunuch it with Vsync off most of the times. But once you start to overkill youll be using v-sync permanently. Problem with v-sync is that it can drop your fps half your refresh rate which can be countered by enabling tripple buffering to get the fps just below the refresh rate.

To make everything short. V-sync is simply a function to let your gpu know of your monitors limitations.
 
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