Graphics cards on Asus motherboard running at half speed problem, need help

Jules123

Jules123

Jules123

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24 Nov 2011
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26
Hi,

I have a problem that my 2 x SLI NVIDIA GTX-590 graphics cards appear to be running at PCI-Express speed of x8 lanes rather than x16.

Indeed the NVIDIA driver control panel says PCI-E x8 Gen 2, for both graphics cards, rather than PCI-E x16 Gen 2.

I have an Overclockers Tyrannosaur PC computer Intel Core i7 2600K Sandybridge System with Asus Maximus IV Extreme-Z Intel Z68 Motherboard plus 2 x SLI NVIDIA GTX-590. Windows 7 x64 with 16GB RAM. AMI BIOS 1.5.1.1041

As instructed by Maximus IV Extreme-Z User's Manual (English) here:
http://www.asus.com/Motherboards/Intel_Socket_1155/Maximus_IV_ExtremeZ/#download

I've put one graphics card in slot 3 (PCIE_X16_2) and the other in slot 5 (PCIE_X16_4) to use the NVIDIA NF200 controller to give x16 lanes of speed. In slot 1 & 2 I have a OCZ RevoDrive3 and a firewire IEEE 1394 card.

I've also benchmarked how fast the CPU can read off a graphics cards. Comes to 2.4GB/s, I think for x16 performance I'm expecting somewhere near 5GB/s. This I did by writing some code in CUDA and using Parallel Nsight to at the profile reports.

Does anyone know why my graphics cards are running at PCI-E x8 speed instead of PCI-E x16?

Thanks for any help,
Jules
 
Hi,

Thanks for the reply but I am not sure I understand. The detailed specs for the graphics card here
http://www.geforce.com/hardware/desktop-gpus/geforce-gtx-590/specifications

Quote "Designed for PCI Express 2.0 ×16 for a peak bandwidth (counting both directions) of up to 20 gigabytes (GB) per second (PCIe 2.0 devices are backwards compatible with PCI Express 1.x devices)"

Admittedly I think the specs are optimistic. Maybe 8GB/s theoretical maximum one-way and I'd expect 5GB/s in practice.

Unfortunately, as mentioned earlier, my tests show I am only getting 2.4GB/s maximum.

Is there something I am not understanding?
Jules
 
Hi Kaapstad

Yes, for games or similar, it doesn't make much of a difference because they use the built-in hardware rasterizers to draw. So things can mostly stay on the graphics card.

In my particular work, I'm combining ray-tracing with film effects, there is a lot of large traffic going to and from host CPU to the graphics cards' GPUs and back again, many times a second.

Your comment
I then added a Revodrive to slot 4 which droped my GTX 590s down to x16/8
Click to expand...

Maybe that's the clue. I have my Revodrive in slot 1 and that could be causing the down-clocking to x8 for my graphics cards in slots PCIE_X16_2 and PCIE_X16_4?

I wish Asus were more flexible here and provided a way to force NF200 to engage. Or at least provide more documentation.


Doesn't look like there is an easy answer?

Jules
 
Here is my bios screen

bios_screen.jpg


It says x16, x16... yes! Unfortunately, in Windows from the NVIDIA control panel

NVIDIA_sys_info.jpg


x8, x8. Something is not telling the truth. Strange? My tests show that the maximum throughput is 2.4GB/s, indicating the latter x8 speed.

Note the revodrive3 x2 in slot 1 does report booting up 5Gb/s.

I don't know :( Thanks everyone for the help.

Jules
 
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