why my tail implementation is much more slower than coreutil ?

[Marco Leise]

tail from coreutils was compiled using the GCC. Use the same
compiler backend (GDC). Any difference that still remains is
from runtime initialization/termination, the overhead of using
a wrapper class around the C routines (for the memory mapping
or printing to terminal) and possibly a faster scan routine for
line endings in the Linux tool. Implementations using SSE to
scan for \n in a block of 16 bytes are possible.

-- 
Marco