> Of course, fork() is not especially fast

fork itself is pretty fast, relatively speaking (unless you have a large virtual address space and 4K pages or similar). fork+execve+process-runtime-initialization is much slower.

On my X201 (anno 2010), with 10000 iterations, sequential fork+exit(0)-in-child+wait takes:

    $ /usr/bin/time ./forkfest
            2,49 real         0,38 user         2,19 sys

while sequential fork+execve("/usr/bin/true",...)-in-child+wait takes:

    $ /usr/bin/time ./forkfest2
           10,99 real         3,10 user         7,94 sys

EDIT: also, My X201 is clocked at 1199 MHz (50%) for power saving reasons