In a 2 CPU system, does it help/hurt/indifferent if the GPUs are plugged in slots attached to the same CPU?

In a 2 CPU system does it help/hurt/indifferent if the GPUs are plugged in slots attached to the same CPU?

Since it all goes/comes to/from main memory, my guess is it does not make a difference.
Perhaps, if DMABUF is NOT used, then it would help if one CPU is doing the UPLOAD, while at the same time the other is doing the IMPORT.

Thanks!

In a 2 CPU system some of your “main memory” will be closer to 1 CPU and further away from the other.

Some PCIe lanes will come into one CPU, some will go into the other.

Ideally, you’d run a VM pinned to cores / threads with some amount of memory allocated from nearby ram, and GPU attached to PCIe lanes on the same CPU socket.

Ah, that’s right. The memory is split too. Didn’t think of that.

So if the use case is to have several LG VMs, it is better to have 1 beefier CPU with sufficient number of PCIe lanes, than 2 weaker CPUs. The UPI links between the pair of Xeons 4114 (4-5 years old) that I have runs at 20.8GB/s in one direction. If I push a couple of [email protected]+ streams through that, it would handle it, but at the cost of considerably reducing the bandwidth and upping the latency for all inter-socket traffic.