Not bad at all, that's approximately the message-passing overhead I measured in C++ on a similar CPU a while back.

I think the main utility for such a benchmark though is to establish a lower limit on theoretical per-message overhead. Any practical system is likely to want to do something interesting with the content of the messages.

But this lets us say "expend an average of at least 5 us of useful computation on each message in order to keep the overall cost of message passing below 10%".