Diagnostic host topology (RunPod EUR-IS-1, CUDA 13.0)

$ nvidia-smi topo -m
	GPU0	GPU1	NIC0	NIC1	CPU Affinity	NUMA Affinity	GPU NUMA ID
GPU0	 X 	NODE	SYS	SYS	64-127,192-255	1		N/A
GPU1	NODE	 X 	SYS	SYS	64-127,192-255	1		N/A
NIC0	SYS	SYS	 X 	PIX
NIC1	SYS	SYS	PIX	 X

$ nvidia-smi topo -p2p r
	GPU0	GPU1
GPU0	X	OK
GPU1	OK	X

$ nvidia-smi topo -p2p w
	GPU0	GPU1
GPU0	X	OK
GPU1	OK	X

$ nvidia-smi nvlink -s
(no output; no NVLink devices or links exposed)

NCCL_DEBUG=INFO NCCL_DEBUG_SUBSYS=INIT,GRAPH,P2P,COLL summary:

- NCCL version 2.27.7+cuda13.0
- GPU path classified as PHB at 48.0 GB/s by NCCL topology
- 4 collective channels, 4 P2P channels, 2 P2P channels per peer
- 0 NVLS channels
- P2P chunksize 131072
- Check P2P Type isAllDirectP2p 1
- GPU 0 -> GPU 1 via P2P/CUMEM
- GPU 1 -> GPU 0 via P2P/CUMEM
- Connected all rings, PXN 0, GDR 1

The first benchmark allocation differed:

$ nvidia-smi topo -m
	GPU0	GPU1	CPU Affinity	NUMA Affinity	GPU NUMA ID
GPU0	 X 	SYS	0-55,112-167	0		N/A
GPU1	SYS	 X 	56-111,168-223	1		N/A

$ nvidia-smi nvlink -s
GPU 0: NVIDIA RTX PRO 6000 Blackwell Server Edition
Device does not have or support Nvlink
GPU 1: NVIDIA RTX PRO 6000 Blackwell Server Edition
Device does not have or support Nvlink