Light-weight threads

[Norbert Nemec]

Robert Jacques wrote:
> Norbert, you are confusing threads with fibers. OS Threads have never 
> been, nor will ever be, "light-weight" in any sense of the word.

What I had in mind were discussions about OSes that make thread creation 
extremely cheap, but indeed: OS threads will probably always carry 
sufficient overhead to leave plenty of room for application-level 
mechanism...

Does anyone know how expensive thread creation is for typical and for 
experimental OSes? How does this compare to the overhead of initializing 
thread-local data? I.e.: How much should one actually worry about TLS?