Question about debugging parallel runs

[Ray Chiang]

I've got a process here at work that sends out jobs to a CPU farm.  In many 
cases, it works fine, sending out as many jobs as can be run in parallel at 
once.

However, I've got one particular target that refuses to run massively parallel 
(say dozens to hundreds).  In order to debug this, I could use some hints in 
debugging.  What I've found so far:

1) Nothing obvious in make debugging output

    Using -d and -p flags to make, there don't appear to be any cross 
dependencies or
    anything that I can think of that would hinder the maximum parallelism.

2) GNU make variables

    MAKE, MAKEFLAGS, MAKECMDTARGETS doesn't appear to give me any
    clues.

3) Debugging using the binary

    I have the make source code and can build and run it fine.  I've already 
tried printing
    out the more obvious internal variables, but that's not enough.

    Can someone give me a medium->high level view of how the code paths for job
    count and parallel execution works so that I can add more debugging output
    for my tests?

I'm not on the mailing list, so please make sure that I'm in the To: field.  
Thanks!

-Ray