| On a machine with dual-GPU and which are connected with NVLink, you will most likely see something like: | |
| GPU0 GPU1 CPU Affinity NUMA Affinity | |
| GPU0 X NV2 0-23 N/A | |
| GPU1 NV2 X 0-23 N/A | |
| on a different machine w/o NVLink we may see: | |
| GPU0 GPU1 CPU Affinity NUMA Affinity | |
| GPU0 X PHB 0-11 N/A | |
| GPU1 PHB X 0-11 N/A | |
| The report includes this legend: | |
| X = Self | |
| SYS = Connection traversing PCIe as well as the SMP interconnect between NUMA nodes (e.g., QPI/UPI) | |
| NODE = Connection traversing PCIe as well as the interconnect between PCIe Host Bridges within a NUMA node | |
| PHB = Connection traversing PCIe as well as a PCIe Host Bridge (typically the CPU) | |
| PXB = Connection traversing multiple PCIe bridges (without traversing the PCIe Host Bridge) | |
| PIX = Connection traversing at most a single PCIe bridge | |
| NV# = Connection traversing a bonded set of # NVLinks | |
| So the first report NV2 tells us the GPUs are interconnected with 2 NVLinks, and the second report PHB we have a typical consumer-level PCIe+Bridge setup. |