@saratoga
thank you for your reply.
I can't say that "make" skip is very smart.
The delay when just one file is changed is 7s.
The delay when nothing is changed is 5s.
I know it's the time used to parse for changed files since there is no delay when make compiles a one-file project. That's really annoying when you develop & compile on just one file of the rockbox project !
P.S. in my config, "make plugins" doesn't work ("*** No rule to make target" error) and I doubt it will change things a lot.
ubuntu@ubuntu-desktop:~/rockbox/build_lua$ time make
CC apps/plugin.c
LD rockbox.elf
OC rockbox.bin
SCRAMBLE rockbox.sansa
Creating rockbox-info.txt
real 0m6.962s
user 0m3.216s
sys 0m3.364s
ubuntu@ubuntu-desktop:~/rockbox/build_lua$ time make
make: Nothing to be done for `all'.
real 0m5.660s
user 0m2.572s
sys 0m2.876s