---
title: "Comment by c-wind on \"Busy polling or events ? Timing one RDMA write, and why perftest says half\" | Hashnode"
description: "The distinction between CQ completion and remote delivery makes the perftest comparison much clearer. One reproducibility detail that could help interpret the 7"
url: "https://hashnode.com/posts/busy-polling-or-events-timing-one-rdma-write-and-why-perftest-says-half/6af159d1709e0bfcfc8f45f1/comment/6af1c872db22570f0bdfd50b"
---

[Discussion](https://hashnode.com/posts/busy-polling-or-events-timing-one-rdma-write-and-why-perftest-says-half/6af159d1709e0bfcfc8f45f1)

Comment [Busy polling or events ? Timing one RDMA write, and why perftest says half](https://hashnode.com/posts/busy-polling-or-events-timing-one-rdma-write-and-why-perftest-says-half/6af159d1709e0bfcfc8f45f1)

[c-wind](https://hashnode.com/@c-wind)

[2d ago](https://hashnode.com/posts/busy-polling-or-events-timing-one-rdma-write-and-why-perftest-says-half/6af159d1709e0bfcfc8f45f1/comment/6af1c872db22570f0bdfd50b)

The distinction between CQ completion and remote delivery makes the perftest comparison much clearer. One reproducibility detail that could help interpret the 7.7 µs event-vs-poll median delta is whether the submitting thread and IRQ/NIC processing were CPU-pinned; even on Soft-RoCE, scheduler placement can shift that wake-up cost. Your caveat about the three-vCPU VM and noisy maxima already points to why it matters.

[Nathanael FETUE](https://hashnode.com/@nathanael-fetue)

[2d ago](https://hashnode.com/posts/busy-polling-or-events-timing-one-rdma-write-and-why-perftest-says-half/6af159d1709e0bfcfc8f45f1/comment/6af1c872db22570f0bdfd50b#reply-6af25d47329931c7e4fa78ad)

Thanks, good catch. They weren't pinned: both modes ran on the same three-vCPU VM with the scheduler free to place the client, the server and the rxe softirq work. So part of that 7.7 µs may be placement rather than the wake-up itself. A pinned rerun (timer on one CPU, softirqs on another) would separate the two; if I run it, the result will be in a later post on CPU cost.

[Nathanael FETUE](https://hashnode.com/@nathanael-fetue)

[2d ago](https://hashnode.com/posts/busy-polling-or-events-timing-one-rdma-write-and-why-perftest-says-half/6af159d1709e0bfcfc8f45f1/comment/6af1c872db22570f0bdfd50b#reply-6af25d68c15324d27885b6a7)

Maybe in part 15.