Need advice about CFX/SLI

Discussion in 'General Hardware' started by kakik09, Mar 30, 2013.

  1. kakik09

    kakik09 Active Member

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    I didn't really know where to put this question since it contained both AMD and Nvidia so I'll put it here :)

    I'm dead-set on having a multi-GPU set-up by the end of this week and I have done my research. But I'm still not sure which card I should get a pair of. I'm buying locally so the prices are different and game bundles do not apply to us (i.e. Never Settle bundles, Nvidia coupons). So here are the cards I'm picking from:
    -Asus GTX 660 Ti DirectCU II 2gb @ approx. 385 USD
    -EVGA GTX 660 Ti 2gb @ approx. 369 USD
    -HIS HD 7950 IceQ X2 Boost Clock 3gb @ approx. 359 USD
    -Inno3d GTX 660 Ti 2gb @ approx. 322 USD
    -MSI GTX 660 (OC Ed) Ti Power Edition 2gb @ approx. 375 USD
    -Power Color HD 7950 3gb (reference design, non-boost) @ approx 300 USD
    -Sapphire HD 7950 Dual-X Boost Ed' 3gb @ approx 367 USD
    -Zotac GTX 660 Ti AMP! Edition 2gb @ approx. 352 USD

    I actually don't mind if I pay slightly more for Nvidia SLI rather than CFX if it means better support and less issues. :)
     
  2. ---TK---

    ---TK--- Ancient Guru

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    Sli more expensive much less issues, xfire less expensive more issues.I went with the sli option and haven't regretted it one bit. There's workarounds for xfire and amd says its working on the problems, but I'd rather play games than tinker tbh
     
  3. yasamoka

    yasamoka Ancient Guru

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    This. Higher performance with CFX as well, but you'll need workarounds and have to set targets (let's say 60FPS @1080p).

    I'm from the other side, CFX here.

    If you're willing to tinker, you'll be more satisfied with CFX's higher performance (until AMD's driver in July which is promised to fix smoothness issues by offering an option). If not, you'll be satisfied with SLI's stability and smoothness, but you should understand that SLI adds a 1-frame delay, which you might be running away from with VSync on CFX (where you get the same 1-frame delay but perfect smoothness as long as you stay above 60FPS).

    Triple buffering reduces latency caused by VSync, and multi-GPU setups inherently use something similar to TB, so at the very least VSync + CFX = SLI (vsync or no vsync) in terms of latency. What happens in terms of latency with SLI once you dip below 60FPS with VSync on, I cannot know, but i dont think they need to add 1 frame then.
     
    Last edited: Mar 30, 2013
  4. Lowki

    Lowki Master Guru

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    I just picked up a 7950 to crossfire with a 7970 about 2 months ago. So far everything has been great with vsync. I play on a 1080p 42 inch hdtv so at 60fps. If that's your target and you use vsync then great. The only problem ive had is with crisis 3 still to this day to get crossfire working properly every time I enter the game I have to turn fullscreen off and back on weird but it works then the game runs beautiful maxed out and even better when you turn shadows and particled down just one notch. I also have a good friend who has a 690 an hes told me hes had to force profiles on games to get sli functioning properly. so as you see both ways you might run into a prob once in a while but if your competent you will be fine. I would say the best performance for you buck right now would be a pair of 7950s and since there the same gpu as 7970 with some shaders lasered off oc it to 7970 clock speed for very similar performance.
     

  5. kakik09

    kakik09 Active Member

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    does nvidia also have any work-arounds in case there is a problem?
     
  6. kakik09

    kakik09 Active Member

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    So um, I didn't really get most of that but can a person really perceive the latency? :s
     
  7. kakik09

    kakik09 Active Member

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    Now I'm very tempted to go 7950 CFX :) should I go down that path, what drivers do you recommend?
     
  8. ---TK---

    ---TK--- Ancient Guru

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    there arent any real problems with sli tbh, maybe having to wait a bit for a sli profile for a game, but you can try afr1 or 2 (sometimes works, sometimes not).
     
  9. Veteran

    Veteran Ancient Guru

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    Yeap no problems here with SLI, I have never ever really had any problems with it since the Voodoo 2 days (first SLI card).
     
  10. Agent-A01

    Agent-A01 Ancient Guru

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    Ive had zero issues with Sli, would recommend it over cf
     

  11. kakik09

    kakik09 Active Member

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    Derp questions, what's afr1?
     
  12. Agent-A01

    Agent-A01 Ancient Guru

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    Its a forceable option in the driver control panel called Alternate frame rendering. 1 and 2 are just different rendering options for applications using sli
     
  13. kakik09

    kakik09 Active Member

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    So, it's some sort of buffering?
     
  14. yasamoka

    yasamoka Ancient Guru

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    Not buffering. It's the de-facto method of rendering, where each card renders alternative frames. Other modes like SFR (split frame rendering) and SuperTiling (exclusive to AMD) do not scale as well as the cards do not know where to exactly split the frame to share the workload equally between the cards in the case of the former, and with SuperTiling both cards need to render the underlying geometry (same case with SFR if I'm not mistaken).

    Disadvantage of AFR is microstutter, which Nvidia have already mostly taken care of. AMD's promised driver update for control over smoothness vs. latency is in July.

    Concerning latency, you might not be able to perceive it, but many can. Depends on how sensitive you are. My point was that if you were running away from VSync on CFX because it adds an extra frame of input lag, be informed that SLI itself adds an extra frame of input lag as well, in order to ensure smoothness on AFR. Both SLI and CFX use something similar to Triple Buffering inherently, which is known to reduce input lag caused by VSync (I do not know how it impacts SLI with no VSync if any).
     
  15. Loophole35

    Loophole35 Ancient Guru

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    At this point I would also suggest SLI over CF but this new option that AMD is putting in their driver in July iirc has me intrigued as AMD has the raw performance if they reduced the micro stutter in the CF setup a that would be a game changer.
     

  16. Lowki

    Lowki Master Guru

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    I'm on the latest 13.3 betas. Been playing bioshock infinite. I usually stay with the latest official betas. The leaked drivers are usually meh. Yeah man you cant go wrong with a pair of 7950s.
     
  17. Lowki

    Lowki Master Guru

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    [​IMG] you also have forcible options with crossfire. you have generic or straight forward options of afr and optimized 1x1 aswell as trying out any other cf game profile to see if works.
     
  18. kakik09

    kakik09 Active Member

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    I've been doing a lot of reading again and many CFX users have been mentioning something called UPLS. What is it exactly? and something about raising the power to +20%?
     
  19. Pill Monster

    Pill Monster Banned

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    ULPS is Ultra Low Power State, a power saving feature on newer cards. When enabled in CFX it can stop GPU #2 from waking up...iirc.


    20% refers to AMD PowerTune which is used for overclocking.
     

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