On: Deep learning box for $1700

[joshu]

Wrong CPU. Only 16 PCI lanes.

[slavivanov → joshu]

Hi, I'm the author. My thought was that running 2 GPUs in a 2x8 config wasn't going to be a bottleneck. Or is it? Apparently my understanding of PCIe is totally off. What would be a suitable CPU (with 40 lanes?) for dual GPU in this price range ($200-$300)?

Thank you for the comments, eventually I can stop spreading my ignorance around :)

[barrkel → joshu]

PCIe lane width isn't normally a significant bottleneck for GPU performance, for games at least. Going from 16x to 8x loses you 1% or so, depending on the hardware. I don't know the bus traffic profile of software being run for deep learning, but it may not be noticeable.

I'd also pick a CPU with more lanes though.

[joshu → barrkel]

It's fine for a single GPU. For multiple GPUs in a deep learning box you want more.

[Toast_ → joshu]

What cpu would you recommend? Would it be better to go with a 2x cpu mobo?

[en4bz → Toast_]

Definitely not since only 1 socket is usually directly attached to the PCIe bus. The best CPU for the money at the moment is most likely an i7 5830K with 40 PCIe lanes. Or you could wait (probably the best idea) for AMD to release it's "threadripper" CPUs tomorrow with 44 lanes and for Intel to release it's new i7/i9 lineup in 2 weeks, also with 44 lanes.

[Toast_ → en4bz]

Cool, thanks for the info.

[en4bz → joshu]

Agreed. This would bifurcate down to 8/4/4 if you wanted to add an NVME SSD or 10Gbit NIC

[polskibus → joshu]

Would you mind to elaborate?

[joshu → polskibus]

It's not enough bandwidth for multiple GPUs.