Compile kernel for various times and problem of too long time consuming

Hi all,
Since I want to evaluate performance improvements by changing just one
file in kernel(noop-iosched) and compiling kernel is too much
time-consuming, I want to know that if I compile kernel for more than
one time, does it take similar time to first time?

I use following commands. If I don't use "make-kpkg clean" for next
times, does it just compile the files which have been modified or it
compile whole kernel package again?

make-kpkg clean
fakeroot make-kpkg --initrd --append-to-version=-some-string-here
kernel-image kernel-headers


Thanks for your help in advance,

--
Amirali Shambayati
Bachelor Student
Computer Engineering Department
Sharif University of Technology
Tehran, Iran