fG, writing for Reverse Engineering Mac OS X:

My tests demonstrate that the syscall interface is definitely much slower in High Sierra 10.13.2. This could lead to some drama, that in most cases, is not justified (I witnessed some minor drama because I released an early chart to see what happened). What my tests appear to point to is that some workloads will be slower but they are probably not relevant unless you are doing millions of iterations. Maybe a 10% impact on your build times is not reasonable at all or you don’t even notice it. The most important thing that users and systems administrators need to do is to measure their specific situation. It’s the only way to be sure if this patch is a problem or not, and build their threat case under this new assumption. One thing is sure, this appears to be here to stay in the medium to long term until all hardware is replaced.

Interesting and varying results, depending on the workload, tested on a MacBook Pro and Mac Pro, running Sierra and High Sierra.