# Mac Thunderbolt4 real Latency numbers > Source: > Published: 2026-09-16 05:41:08+00:00 Hello All, Not posted in a long time. but I cant find answers anywhere else. I have been following the AI clustering topics about USB4. **I need someone to help get me real latency numbers for Mac Thunderbolt RDMA.** Can someone run ib_read_lat, ib_write_lat and ib_send_lat or some equivalent on a 2 node setup. I need to know if it is real RDMA or just really good software RDMA. My understanding right now is that there is no way that thunderbolt can bypass the CPU/kernel and go to the GPU vRAM with a zero-copy. There is a limit to how low they can get without adding a RDMA chip to the USB port, which apple might do. If results are >5 than it is just software RDMA. If results are lower than they must have RDMA hardware. If it is <2uS then we are really cooking. Notes: I have tested both `thunderbolt-ibverbs` and `OdinLink-Five`. and they are good but most of the improvements they get in latency is from enabling busy polling. I am running it with Strix Halo and getting 7.8uS over TCP. I want to know if Apple is just doing the same trick. `sudo sysctl -w net.core.busy_poll=100` `sudo sysctl -w net.core.busy_read=100` I look forward to getting real numbers for latency. [boatman](https://forum.level1techs.com/u/boatman) 2 Update: I was not able to get numbers but I can confirm that the USB RDMA on Macs is just good software. not real RDMA hardware offload.