As baselines, the median warmstart latency in AWS, Google, and Azure were about 25, 79 and 320 ms (respectively) across all invocations.
If, like me, you are using AWS Lambda or its competitors, this paper by Liang Wang et al is worth a careful read. Lots of well-done measurements of performance, isolation, instance lifetimes and more.
Functions as a service behave differently than the servers we’re used to, so be sure and understand your platform and how it behaves!
via http://pages.cs.wisc.edu/~liangw/pub/atc18-final298.pdf (PDF)