Thanks for quick response and for informative answers, especially 
thanks to Antoine Pitrou/Amaury Forgeot.

p.s.
By seting bigger range - range(15) and elements = 1000, I was able to 
get speed-up factor up to 1.8. Wow, I`m amazed :-)
Good library, keep it up.
BTW, about warp-up,- forking first processes. User can forget 
to "warpup" pool. It would be cool if pool somehow warm-ups itself in 
initialization phase (in step mul.Pool(processes=mul.cpu_count())).
Maybe you can define another initialization parameter=function ? (if 
not None, first processes should be spawned, not waiting map function) 
or something like that. But it is only cosmetics :-)