Why is it "fake" here, while referenced as "usermode" below?

because I was looking at the wrong function header and caught my mistake everywhere but here.

Should this be .Fx?

looks like .Fx to me :)
But I changed that while you were making this comment, so great minds :)

typo: single

As a non-native speaker, I'm not sure whether this sentence is missing a predicate or it's "structures" that "are emulated".

It's probably due to my ignorance, but I don't understand what "the it" here is.

I think we need to use a space to separate numbers from units.

I think it would be good to link eventtimers(4) here, or even more synchronize them.

This makes it sound a little bit like wall time is simply counted up here?

Maybe something like "The main clock is used to refresh timecounters(4), and ..." ?

stathz should not be documented, it should be removed.

To have any statistical strength, statistical sampling must sample approx 0.1% of all instructions without aliasing effects.

Running stathz at tens of MHz (~= NCORE*CPUCLOCK/1000) is maybe doable, but avoiding aliasing is impossible with the deep pipelines and telegraphic memory service of modern hardware.

That is why modern chips have hardware performance counters.

The profiled libraries should be converted to gcov instead.