Questions about the WS X299 Sage motherboard and PEX8747 PLX chip

[anandtechreader]

Hello, I am building a high-end workstation for research not for gaming. I plan to do high performance CUDA computations with multiple GPUs. Running the GPU at x16 makes a difference compared to running at x8. The problem is that even the Threadripper and Intel i9-7900X do not support PCIE3.0 16x16x16x16.

I came across a WS X299 Sage motherboard with dual PLX chips. Has anybody used it? I cannot find benchmark results related to this board.

I need some expert opinions. Could you please help? Please refer to:

http://dlcdnet.asus.com/pub/ASUS/mb/Socket2066/WS_X299_...

On p.119, there is a block diagram. I noticed the following:

- None of the PCIe X16 slot is connected directly to the CPU.
- They seem to operate at 100MHz PCIE 16x/8x

1. Does that mean by adding two PLX chips, none of the PCIe x16 card/slot can operate as fast as if they were directly connected to the CPU?

2. How efficient is that PEX8747 PLX chip? Will the latency affect performance?

3. If I use only 1 or 2 GPUs operating at PCIe 3.0x16x16, do I gain better performance using this MB or standard MB likes Gigabyte X299 Aorus Gaming 9, Asus X299 Prime-A or MSI X299 SLI Plus MS-7A93 in the case of using 7900X and Gigabyte X399 AORUS Gaming 7, MSI X399 Gaming PRO Carbon AC or Asus Prime X399-A?

Am I right that I can only plug in one NVMe SSD M.2 to this motherboard? I may need two SSD.

Thanks.

 

[sinisterDei]

I don't know about your PLX chipsets, but I do have a different angle.

It sounds like you're considering dropping a decent boatload of cash on a system if you're planning on running quad GPUs on a high end workstation.

You may just consider moving up a hierarchy to the Epyc platform and use something like this: https://b2b.gigabyte.com/Server-Motherboard/MZ31-AR0-rev-10#ov

That'd get you 5x PCIe X16 slots, 4x of which are x16 electrically, and all connected directly to the CPU. It's also got a ton of storage connectivity and a M2 slot for some NVME.