[plt-scheme] embedding: scheme_check_threads question

Hi all,

I've got a bit confused reading the docs on scheme_check_threads:
http://docs.plt-scheme.org/inside/threads.html#(part._threadtime)

I've noticed that plt threads running in fluxus tend to get starved in
an erratic fashion. The answer seems to be this function, but I'm a
little confused by the timer example, is the general idea to
periodically call it while threads are active? (using
scheme_notify_multithread).

I have a periodic update loop (the interpreter gets run once per frame)
so I've tried calling scheme_check_threads every update without much
luck, however, calling it 100 times in a loop every frame (!) seems to
fix my problem by giving enough time to the threads - but also causes
lockups in other situations. 

What am I missing?

cheers,

dave