REDDIT · REDDIT// 2h agoBENCHMARK RESULT

RTX Pro 6000 P2P Bandwidth Slumps

A dual RTX PRO 6000 Blackwell Max-Q setup on an Asus W680 Pro shows an odd inversion: peer-to-peer bandwidth drops to about 6-8 GB/s with P2P enabled, but reaches around 20 GB/s with it disabled. The poster says latency is fine, Resizable BAR must stay off for the system to work, and `nvidia-smi topo` reports `PHB`, suggesting a platform-level routing issue rather than a simple GPU limit.

// ANALYSIS

This looks less like a bad benchmark and more like a PCIe topology problem wearing a GPU costume.

–`PHB` usually means traffic is traversing the CPU/root complex, so direct GPU-to-GPU transfers may be constrained even on Gen 5 x8 links
–NVIDIA docs note that PCIe peer-to-peer performance can be hurt by ACS, IOMMU, and routing through the root complex, all of which can crush bisection bandwidth
–Having to disable Resizable BAR just to keep the pair stable suggests the board is already in a compromise configuration
–The surprising part is not that P2P is slower, but that host-mediated copies can beat it when the platform cannot provide a clean peer path
–For dual-GPU AI rigs, this is a reminder that motherboard BIOS, chipset behavior, and slot topology can matter as much as raw GPU specs

// TAGS

gpubenchmarkpcieworkstationnvidiartx-pro-6000-blackwell-max-q

DISCOVERED

2h ago

2026-04-21

PUBLISHED

4h ago

2026-04-21

RELEVANCE

7/ 10

AUTHOR

ThatsMyNameDude