https://www.quora.com/Is-FreeBSD-faster-than-Linux
Yes, FreeBSD is faster than Linux. Yet, Linux is faster than FreeBSD. So it depends on what you’re talking about. The TL;DR version is: FreeBSD has lower latency, and Linux has faster application speeds.
These two statements (FreeBSD has lower latency; Linux has more raw power) have been true for two decades now. But they may change just a bit soon! There are some “BSD-inspired” networking improvements to Linux starting with the 4.16 kernel. Facebook has in fact employed engineers for the sole purpose of trying to get Linux up to speed with FreeBSD for the web, and some parts of 4.16 are the fruits of their labors.