🔧 How PCIe, NVLink, and NUMA Topology Affect GPU Scheduling Outcomes

GPU topology changes what “8 GPUs” really means: NCCL step time, multi-node InfiniBand efficiency, and inference p99. NVLink can hide bad PCIe wiring. 

NUMA never does. On PCIe-only cards like NVIDIA L40S (PCIe Gen4 x16, NVLink: No), the scheduler must respect PCIe and socket locality, or you’ll buy GPUs and get bus contention. 

GPU topology is...