Multi-Threaded make

[JD]

While building the kernel from source RPM, I run
the command ps -ef | grep make in another terminal,
and I do see that 4 make processes are running, with
each one building objects for a different kernel source
directory.

However, something else seems to be single threaded
which is causing the huge delay in finishing kernel build.

I found that when I run top to see the upper-most
cpu consumers, I see only one cc1 process at the top.

So I ran ps again to see how many cc1 processes there
are.

Always - just one cc1 process.

I would expect to see anywhere from 1 to 4 cc1 processes
at a time. But that is not the case.

What is forcing only a single instance of cc1 at a time?

I hope the devs can have a look at either the compiler
tools or the make util.