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Why is link speed only x8?

Discussion in 'AMD / ATI' started by fullinfusion, Apr 4, 2013.

  1. fullinfusion

    fullinfusion 1.21 Gigawatts

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    Sorry for this question, but can someone help me understand why this motherboard is only running @ x8 speed with both my 7970's installed on the maximus IV extreme-z68 board?

    Under details


    [​IMG]
     
    Last edited: Apr 4, 2013
  2. 95Viper

    95Viper

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    Did you try putting a load on 'em, with the render test (the little "?" mark beside the Bus Interface info)?

    The cards are probably in the 2D energy savings condition.
     
  3. fullinfusion

    fullinfusion 1.21 Gigawatts

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    Yes I have.

    specs say x16 x8 x8 or x16 x16?

    manual says slot 1 and 3 for best results in cross fire mode. It's kinda stumping me.

    [​IMG]
     
    Last edited: Apr 4, 2013
  4. 95Viper

    95Viper

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    Well, if I am looking at it right... that board will have one slot at x16 or two at x8.

    That is what I gather by looking at this chart from the manual.
    picture1.png

    Have you ever crossfired before with different results?

    Maybe someone else will have more insight into this, I have not used but a single(meets all my needs) for quite a while.
     
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  5. newtekie1

    newtekie1 Semi-Retired Folder

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    Yep, that is exactly it.
     
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    Crunching for Team TPU 50 Million points folded for TPU
  6. fullinfusion

    fullinfusion 1.21 Gigawatts

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    so does Z77 run the same?
     
  7. newtekie1

    newtekie1 Semi-Retired Folder

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    It all depends on the board. On socket 1155 Intel only provides 16 PCI-E lanes to graphics. So they are usually split into x8/x8. However, there are some boards that use PCI-E switches to give x8/x8/x8/x8 or x8/x16/x16. However, those extra slots are still sharing the original 16 lanes to communicate with the CPU. So even on your board, those two x16 slots running off the nf200 switch are actually sharing an x8 link to the CPU.
     
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  8. Frogger

    Frogger

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    "The NVIDIA NF200 chip supports 32 PCI-E 2.5GT/s lanes.
    Here is how it works, NF200 takes the native 8 lane 5GT/s bus and doubles the bandwidth to 16x5GT/s so you would have 32 lanes of 2.5GT/S PCI-E bus for 16x SLI. Do not be fooled it doesn’t add PCI-E lanes; instead it splits the ones already present and adds bandwidth. It is really great at consolidating and making sure the proper devices are fed full bandwidth. Although we have 32 lanes of PCI-E bandwidth GIGABYTE says the board only supports 3-way SLI. This is most likely because 4-way SLI would be 8x each card and performance would take a hit. This board also supports CrossFireX which is the ATI/AMD equivalent for SLI technology.
    On this board ALL the PCI-E lanes from the processor are fed directly into the NF200. On many X58 boards and P55 boards, only a portion of the PCI-E lanes are fed to the NF200, the reason is that USB3 and SATA6G work off the high speed PCI-E bus, but this board is one of the few exceptions. The new P67 PCH connects to all of these devices through a secondary PCI-E bus, that has its own clock generator, and its own set of 8 PCI-E switches. The PCH then communicates to the CPU through a high speed 20GB/s DMI interface. The NF200 connects to the 4 PCI-E slots through 2 switches.
    Many people have mixed views of the benefits of 16x/16x vs 16x/8x SLI, regardless the NF200 is needed for proper SLI on LGA 1155 motherboard. This motherboard will probably perform exceptionally at SLI with the NF200 because all the PCI-E lanes from the processor are used solely for the PCI-E slots."

    hope this helps
     
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  9. Law-II

    Law-II

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    Hi

    For dual PCIe x16 would need to run skt 1366 x58 or skt 2011 x79 [*some limitations still apply electrical x4, x8 and x16]

    atb (all the best)

    Law-II
     
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  10. fullinfusion

    fullinfusion 1.21 Gigawatts

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    Well thanks for all that :respect:

    So really there isn't much of a benefit so far from board to board running 16x16 or 8x8 :confused:
     
  11. Zubasa

    Zubasa

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    It have been tested multiple times that GPUs just do not require that much bandwidth in games.
    Even if the card is running on 4x the effects on performance is minimal. Latency makes a lot more difference than bandwidth in this case.
     
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  12. GamerGuy

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    Yep, for full, or near full bandwidth, you'd want IB + Z77 mobos (I believe) and LGA2011 CPUs + X79 mobos. Here's a screenshot of my 3x HD7970 on my R4E:
    [​IMG]
     
  13. EarthDog

    EarthDog

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    NF200.... wasnt that on older boards? Isnt it all handled by the PLX chip these days?

    EDIT: I see a Z68 based board.

    EDIT2: Isnt that the PLX chip down by the 4x slot at the bottom?
     
  14. Law-II

    Law-II

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  15. hckngrtfakt

    hckngrtfakt

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    So to answer the original question, yes running crossfire (7970's) at 8x-8x is perfectly normal for that board. ;)
     
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  16. GamerGuy

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    Thanks, that was.....informative.:) And yet, at the same time, quite confusing.....and no, I ain't too bright especially with such tech stuff. So, does that mean that as of now, only X79 does have true multi GPU full bandwidth support? Is my screenshot an accurate representation of the bandwidth on my setup?
     
  17. EarthDog

    EarthDog

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    TPU has done a review on 8x/8x with 680 and 7970 and its average performance loss across all games at 1080p was 1%.
     
  18. Law-II

    Law-II

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    Hi

    Yes; *true multi GPU full bandwidth [at this time]

    Yes; *Full Dual support [x16 x16 dual, x16 x8 x16 tri, x16 x8 x8 x8 quad] Asus ROG Rampage IV Extreme

    nb: Nice Rig :toast:

    atb

    Law-II
     
  19. cadaveca

    cadaveca My name is Dave

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    Even with PLX chip onboard, ASUS feels x8/x8 native is better.

    [​IMG]
    I have tested many boards now with PLX8474, and on some of those boards, x16/x16 with PLX is actually faster, so this confused me. With the MVE, no matter what you do, as long as more than one GPU is installed, you have the top slot @ x8, directly connected to the CPU.

    that was just with a single card, not multi-GPU, so doesn't really mean a thing. Testing x8, without multi GPU, is kind of silly...no board supports just x8 for a single GPU, all are x16, except one or two mITX that only give x4 PCIe.
     
  20. brandonwh64

    brandonwh64 Addicted to Bacon and StarCrunches!!!

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    I have a Z68 and it shows PCIex 2.0 X16 with my 7970

    With two 7970's it will be at x8 2.0

    [​IMG]
     
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  21. EarthDog

    EarthDog

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    Right, but they each get 8x bandwidth so why would the story be different? Am I missing some overhead or something?
     
  22. cadaveca

    cadaveca My name is Dave

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    Yep, just overhead for inter-GPU communication(I believe). With the Crossfire bridge only offering 1 GB/s, three and four GPU configurations connecting to the main card with only one bridge, may run into bandwidth issues.

    The perfect example is x16/x4 PCIe...5-10% performance lost at most for a single card. But try Crossfire, and you can lose up to 50% compared to x8/x8.

    I'm not sure why, but it does seem to be confined to DX10 and DX11 apps, and maybe because some data from each frame is shared for the next..or something...GPUs are not my department of TPU.:p
     
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  23. fullinfusion

    fullinfusion 1.21 Gigawatts

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    Dave, im on the road atm and seen others talk about a video you posted on cross fire problems. Would you be kind and link me to it :)

    And thanks for all the info guy's
     
  24. Aquinus

    Aquinus Resident Wat-man

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    GPUs aren't the only thing that uses PCI-E. You could easily have a RAID card that uses 4 lanes and you have to go down to x8/x8 to run the GPU and the RAID card together, so I wouldn't call it silly.
     
  25. cadaveca

    cadaveca My name is Dave

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    When there's x16/x4 boards for exactly that sort of config(with x4 run via chipset), yeah, it'd be a silly purchase decision, IMHO.



    Sent a PM.
     
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