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S.L..O...W PCIE bus with single GPU, 6970/7970 in any slot, why??

post #1 of 6
Thread Starter 
Hello to all, this is my first post although I've been reading OC Forum for a long time. I have a real love for fast hardware and AMD GPUs and use 6870 Barts, 6970 Cayman, and 7970s.

But, I've just found that my PCIE bus bandwidth is limited to 1.6GB/s, each way, where it should about 6 GB/s using x16 v2.0 slots. I've tried every card in every slot, one at a time, and always get the same numbers. I have also updated and reinstalled main board bios and drivers, Intel drivers, AMD drivers, and used every BIOS configuration that might help. PCIE data rate is measured using programs like PCIeBandwidth.exe and PCIspeedtest.exe from AMD. What I get is:

PCIe x4 slot, transfer rate=1.3 GB/s (read and write) (one card)
PCIe x16at x8, transfer rate=1.65 GB/s (read and write) (requires 2 cards)
PCIe x16 at x16, transfer rate=1.65 GB/s (read and write) (one card)

The x4 slot is always just a bit slower. System: ASRock z68-Extreme7 motherboard, 5 PCIE slots, one for PCIE v3.0, 3 for multi GPUs (x16, x16, 0) or (x16, x8, x8) and a dedicated x4 speed slot, with Windows7 x64. The main board also uses PLX PEX8608 and NL200 chips to increase the number of PCI lanes.

I would love to know if anyone has seen similar problems with PCIE performance, or if anyone can verify that the new AMD drivers (I'm using the 12.3 driver dated February 16 at AMD) are running at full speed (5 to 6 GB/s). I think it is rather strange that all the slots run the same speed. I don't think this would be a hardware design problem but it's really hard to know until the problem is solved.

BTW, I also checked using GPU-z which says the cards are configured as x16 v2.0 when in the x16 slots.

It's been a frustrating week searching for clues and any help is very much welcome.

Many thanks,

relee
Edited by relee - 3/2/12 at 4:27am
post #2 of 6

If you get those readings from GPU-Z, ignore it. You will see the fullspeed when the cards are in 3D clocks running applications in fullscreen.

 

 

900x600px-LL-dc45537b_Capture.jpeg

 

ケンジ
(16 items)
 
  
CPUCPUMotherboardGraphics
i7-3960X i7-980X GA-X79-UD7 / GA-X58A-UD9 7970 + 465 
GraphicsRAMRAMHard Drive
2x 6990 + 580 16GB 2133 MHz 24GB 2000 MHz 120GB x 2 RAID0 
Hard DriveHard DriveCoolingCooling
120GB x 4 RAID0 Raptor 300GB x 2 RAID0 CPU-370 CPU-370 
CoolingCoolingOSPower
VID-AR699 EK FB X58A-UD9 Win 7 Ultimate x64 1500W / 1250W+1200W 
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ケンジ
(16 items)
 
  
CPUCPUMotherboardGraphics
i7-3960X i7-980X GA-X79-UD7 / GA-X58A-UD9 7970 + 465 
GraphicsRAMRAMHard Drive
2x 6990 + 580 16GB 2133 MHz 24GB 2000 MHz 120GB x 2 RAID0 
Hard DriveHard DriveCoolingCooling
120GB x 4 RAID0 Raptor 300GB x 2 RAID0 CPU-370 CPU-370 
CoolingCoolingOSPower
VID-AR699 EK FB X58A-UD9 Win 7 Ultimate x64 1500W / 1250W+1200W 
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post #3 of 6
Thread Starter 
Ken1649,

Thanks for the table. The numbers I get are from measuring real data over the PCIE bus, about 1.6GB/s, very slow.
PCIe 2.0-x16 should be 8GB/s theory ( your table) or about 5.5 to 6 actual.
Clocks are OK too, I see 1220+ Mhz core on my 7970 when I run programs. These cards are killers, thus the PCIe problem is a shame.


But, I found the problem, the ASRock mobo does not run as stated in the manual. the Extreme7 Gen 3 has a single dedicated socket (slot 2) that supports PCIe 3.0 x16, that socket runs fine at full bandwidth, so? not the AMD drivers:thumb:thumb:

It also has 4 more PCI slots (1,4,5,6) that (by the manual) run PCIe2.0(x16, x16) or PCIe2.0(x16, x8, x8). All these slots are running very slow. They use a special PCIe switch and NF200 chip for these slots, which I think is causing the problem.

But you are right about GPU-z being misleading, it says everything is fine and reports the slots working at x16.

Beyond that it gets technical, the bus is running x16 smile.gif but the bus is refusing to use what is know as burst mode mad.gif . Single write mode on PCIe requires 5 cycles and is slow. 8GB/s divided by 5 is 1.67 GB/s, exactly the numbers I get wink.gif . Clearly a hardware problem.

I should move this to the thread for ASRock motherboards, now I know where the problem is.

Thanks,
Edited by relee - 3/10/12 at 8:10pm
post #4 of 6

nVidia nF200 does improve many things with the tax of latency. thumb.gif

 

If we want to have everything fast, have to pay more with X79 smile.gif


Edited by Ken1649 - 3/11/12 at 9:24am
ケンジ
(16 items)
 
  
CPUCPUMotherboardGraphics
i7-3960X i7-980X GA-X79-UD7 / GA-X58A-UD9 7970 + 465 
GraphicsRAMRAMHard Drive
2x 6990 + 580 16GB 2133 MHz 24GB 2000 MHz 120GB x 2 RAID0 
Hard DriveHard DriveCoolingCooling
120GB x 4 RAID0 Raptor 300GB x 2 RAID0 CPU-370 CPU-370 
CoolingCoolingOSPower
VID-AR699 EK FB X58A-UD9 Win 7 Ultimate x64 1500W / 1250W+1200W 
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ケンジ
(16 items)
 
  
CPUCPUMotherboardGraphics
i7-3960X i7-980X GA-X79-UD7 / GA-X58A-UD9 7970 + 465 
GraphicsRAMRAMHard Drive
2x 6990 + 580 16GB 2133 MHz 24GB 2000 MHz 120GB x 2 RAID0 
Hard DriveHard DriveCoolingCooling
120GB x 4 RAID0 Raptor 300GB x 2 RAID0 CPU-370 CPU-370 
CoolingCoolingOSPower
VID-AR699 EK FB X58A-UD9 Win 7 Ultimate x64 1500W / 1250W+1200W 
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post #5 of 6
I'd say it's your motherboard, but because I cannot see which brand / model you have, I really cannot help you much..

If you Google your motherboard with PCIe in the search you may come up with an answer to "Why".

Google Search + A Little Time Researching = Solutions / Answers...
It's a billion dollar search engine, use it..
Edited by _GTech - 3/11/12 at 9:21am
The Rock
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The Rock
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post #6 of 6
Relee,

I am having very similar problem with Asus RAMPAGE IV Extreme i7 X79 LGA 2011 DDR3 PCIE motherboard and 7970
it's so slow for RAM to GPU transfers compared to same 7970 in Intel Core i7-2600K 3.4Ghz 8MB Cache 32NM LGA1155 (instead of faster)

Discovered more about that in last few weeks?

Thanks

Pierre
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