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

Software & Operating Systems Looking Glass
1

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!

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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.

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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 4K@60Hz+ 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.