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OCed 7970s and 4K

Discussion in 'AMD / ATI' started by Champ, Aug 15, 2014.

  1. Champ

    Champ

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    So could I sufficently run 4K with two heavily clocked 7970s?
     
  2. The Von Matrices

    The Von Matrices

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    You could run it, but I would highly recommend against it. This isn't due to the raw number of frames per second you could get. Rather, the issue is frame time variance.

    All AMD GPUs that use Crossfire bridges (including the 7970) suffer heavily from frame time variance issues with >4MP displays and Crossfire. Even though AMD has within the last year added some fixes for a small number of games, using Crossfire with older cards and >4MP displays is still fundamentally broken. This is the reason AMD replaced it with XDMA on the 290 series.

    With a 4K (8MP) display and Crossfire 7970s, you can still expect frame time variance of greater than 50% with the "fixed" drivers. For reference, less than 20% is considered acceptably smooth. In other words, games will look like a stuttering mess if you use 7970 Crossfire to drive a 4K display no matter how many frames per second FRAPS or some other utility shows you. Of all AMD cards, only the 290 series performance acceptably in Crossfire with >4MP displays in regards to frame time variance.

    I have 3 7970s for a 5760x1200 resolution (7MP), and I can't stand to use them for Crossfire because it actually looks less smooth than a single card at a lower framerate. If I was in your situation I wouldn't get a 4K display unless you're happy with a single 7970 or you can replace your system with AMD 290 series card(s) or modern NVidia card(s).
     
    Last edited: Aug 15, 2014
    yogurt_21 and Champ say thanks.
  3. Champ

    Champ

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    I forgot that. Thanks for the reminder

    So I'm reading for 4k I should go with the r9s and the 290 at that. Its said they are cheaper, easier to cool, comsume less power and have a higher ceiling. The board I want only supports 2 way crossfire. When you can only have two, are the 290s still the best bet?
     
    Last edited by a moderator: Aug 15, 2014
  4. GhostRyder

    GhostRyder

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    Well thats not entirely true about then using less power the rest is kinda moot. As for cooling with any of the aftermarket coolers cooling is a breeze and you will not have to worry about thermal throttling or anything like that. With 4k one thing to note is that there are some issues with the Samsung and Asus 28 inch 4k monitors due to the choice in panel that has not been completely resolved yet while the AOC one for sure seems to be working and a few others. As far as price to performance, yes you could with two R9 290's especially if you overclock them reach high-ultra settings on a 4k display.

    Between the options if your looking for a good price to performance and 4k, that will probably be the best option.
     
  5. Champ

    Champ

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    I just brought the aoc monitor and it looks promising. I just need the horsepower to do it justice
     
  6. GhostRyder

    GhostRyder

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    I run on 3 R9 290X cards stock and overclocked (Just for the purpose to see how much more the overclock gave me). The cards gave me more than enough to keep 60+ FPS ultra in most games I play minus a few (Crysis 3 I keep MSAA down to 2x and I can keep 45+FPS).

    Try checking these reviews out and you can see what to expect. Also if you bump the core clock to 1100 and the memory clocks up you will notice some nice numbers at 4k.

    http://www.guru3d.com/articles-pages/radeon-r9-290-crossfire-review-benchmarks,21.html
     
  7. cynan New Member

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    Do you know for certain that 7970s in crossfire would still have the same degree of frame time issues on single-tiled 4k monitors? The first 4k monitors had 2 panels as the timing controllers driving them could not support the requisite bandwidth, and were effectively seen as multiple displays by the GPU... As such, perhaps the most egregious frame time issues of which you speak is a question of multi-display support, not resolution?

    Has anyone tried something like crossfired 7970s with single tiled monitors over 4MP?
     
  8. The Von Matrices

    The Von Matrices

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    I'd be curious to see someone test it, but I wouldn't expect anything different. The limitation is not due to multiple displays, it is due to the limited bandwidth of the interconnect. The crossfire bridge only provides 900MB/s, which is only enough to transfer the framebuffer of a 4MP display at 60Hz. For a higher resolution display, the frames must go over the PCIe bus, which is where the variance is introduced.

    As a counter example, If you ran 3 1280x1024 displays on crossfire 7970s you should have no frame timing issues because the resolution is low enough that the interconnect is not saturated.
     
    Last edited: Aug 15, 2014
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  9. Verviticus New Member

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    I run 2 X Gigabyte 7970 Ghz edition cards in crossfire on my 4k display @60hz, it's an asus PB287Q, running on displayport 1.2, a single cable. It runs great. There is a noticeable improvement in most games. Most games still run on high or ultra. Never seen this timing issue I've read about, no weird tearing or whatever, I usually run v-sync if that makes a difference....I tried BF4, WOT, Crysis 3, Hawken, Tribes Ascend, Mass Effect, Bioshock Infinite, best of all skyrim....maybe one or two more. None have had any issues and work flawlessly. WOT I have to play at medium settings to get running smooth at 4k.

    I always leave textures on ultra and AA on max and drop other things down like effects/shadows/terrain if I have to, I like having smooth models. You CANNOT see the pixels. If things weren't so unnaturally straight and angled you might believe they were real pictures in some games. The coolest thing is it makes older games look amazing. Kind of like installing quake II on a modern machine and running everything at super-ultra and finally seeing what it could have looked like if the hardware was available back then. You just can't see pixels anywhere....maybe my eyes are getting old.

    I actually came here looking to see if getting a third card would give me any benefit. I have a 1200 Watt PSU already and a motherboard that supports three way.

    It's a MSI msi z77a-gd65, its running 8x/8x right now but still much better than single at 16x. If I add a third card it will be 8x/4x/4x. VERY LITTLE INFO online on these more advanced configurations. I might have to try it just for the sake of not finding any reviews of 4k gaming on 3-way crossfire. Or the effects of dropping down to 4x/4x on the two additional cards.

    As far as I can tell on pci 3.0 there is only a few percent difference between 16x and 4x as far as frame rate goes.


    Lots of people talk like they know what their doing, but I have seen very few people put their money where their mouth is and buy the hardware and show some real results. Too many armchair engineers these days.

    If anyone has any real experience I would love to hear from you.

    I use GV-R797TO-3GD GPU's if anyone has one they're willing to donate it to the cause. I might even be willing to pay you if I like the cut of your jib, and I don't think I'll get stuck with a junk card.

    Thanks!
     
  10. Verviticus New Member

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    Yes, and 1100mhz stock overclock is plenty.
     
  11. Champ

    Champ

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    Well I have two 290 that I'm gonna cool and clock the crap out of now
     
  12. MxPhenom 216

    MxPhenom 216 Corsair Fanboy

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    2 GTX970s or 980s.
     
  13. Verviticus New Member

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    The lower card never seemed to be an issue, but the upper card is always getting really hot. Sometimes I can hit 80c for short periods of time. Limited my OC potential. I swapped cards around and still upper card heat issues. There is a full single space between the cards so they are not touching.

    Biggest issue I had was the SATA ports. Most mobo have them coming straight up off the board which got in the way of the second GPU. (broken one SATA port even). Since then I got my current mobo which has the SATA ports coming off the edge of the board. Now I have all the space in the world for extra GPU.


    Keep the heat and configuration in mind when your building the setup.
     
  14. Verviticus New Member

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    I should mention that the only game I really have heat issues is WOT....not sure why its such an inefficient game that always makes both GPU's run at 100% the whole time...
     
  15. The Von Matrices

    The Von Matrices

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    I wish I could say I have the same positive experience as you (and I am running the x8/x4/x4 triple crossfire configuration you describe minus the 4K monitor). I'm curious to know what your framerates are that you consider smooth. I used to think I could only run games at medium settings, but after enabling a frame rate counter I realized that the games were actually running at 100+ FPS and if I increased the settings enough to get about 60 FPS it became a stuttering mess due to frame pacing issues. In that case the extra cards don't matter since a single card at 45 FPS looks just as smooth as three cards at 100 FPS. BioShock Infinite is in my opinion the worst offender in this regard and I disable Crossfire whenever I play the game. Although you just gave me an idea to try two cards instead of one or three; I wonder if that would be better. I'll have to experiment.
    The game is probably running at 1000 FPS. You can set a framerate cap (probably somewhere in the game settings) and the cards will run cooler and save energy with no perceptible difference.
     
  16. URBAN303

    URBAN303

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    Personally my 280X CrossFire works wonders !! even 3x screens fullhd resolution Eyefinity = 5760x1080 ! most games work wonders ;)

    Few games do not work best with the CFX. Indeed simulations of kind "Assetto Corsa" and "EuroTrucksSimulator2" do not seem compatible with Crossfire but with one card they are very good and the second would be useless for those games.

    For WoT to simply activate the VSynch in the settings of the game.
    On the garage of game my cards are at ~70°C while in game they dipped to around 64°C.

    I would add that in Crossfire MUST activate the vertical synchronization to ease sync between the two video cards ... it is better although some games seem to work fine without VSynch enabled.
     
    Last edited: Oct 12, 2014

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