PFC · Priority Flow Control
An Ethernet mechanism that pauses traffic to prevent packet loss, making RoCE lossless but risking head-of-line blocking.
Current numbers
May 2026MRC released as an open OCP spec (OpenAI + AMD/Broadcom/Intel/Microsoft/NVIDIA): RoCEv2 extension with per-packet spray, SACK, optional trimming, PFC-off; production-proven at 50k–75k-GPU scale before publication
400Gspeed at which Meta ran production RoCE PFC-only on the back-end, leaning on topology over loop tuning