I am compiling the Linux kernel in a VM(virtual box) with 2 out of 4GB and 4 out of 8 CPUs allocated. My initial compilation took around 8-9 hours, and I was using make -j4 optimisation too. Now I added a simple system call to the kernel and just ran the make -j4 and and it has been compiling for the past 3 hours. I thought that after the initial compilation, make would only compile the small changes but it seems to be compiling everything (mostly the drivers). Is there any way I can speed up this compilation process?
For example, is there anyway by which I can disable some of the drivers that I don't really need, for example if I just want to implement a simple system call, I don't really need all the networking drivers, and maybe that would speed it up? i.e. I just want the bare minimum functionality for my kernel to test my system calls.