Thank you 1nickt for the help!

I'll go through it tmr.

Earlier today, I modified the code, to instantiate new Parallel::ForkManager objects three times in the script.

then have them run serially, forks for 1st subdirectories, forks for 2nd subdirectories, last group of forks for the main directory

At the point, I still thinking it's wasn't optimize, as the 1st and 2nd subdirectories should be run in parallel as well.

but i havent quite figure out how to get there