Actually what you will get for calling Win32::Perflib is a massive structure made of hash of hash of hash ... up to 7 levels. This structure contains everything that the performance monitor service of Win32 is able to collect, and that includes global cpu load (per CPU on a SMP system, but there maybe also a grandtotal) . Your problem will be to find where it is !

I found that the perflib struct was almost impossible to understand so i had to test thing many times in order to get the info i wanted from it . Dave Roth has some example scripts on his "roth consulting" site, he wrote the "Win32 perl programing" New Riders book (which i don't recommand by the way, it's close to useless )

I don't think you can assess the cpu impact of a job (that is a pool of process) through perflib, and you will still have to add the load of the different forked process.

About forking without Win32::Jobs, the only thing i can say is: even IPC::Open3 didn't work very well for me and that's standard in the active state distribution ! You can't even pass filehandles to the forked process. My feeling is that if you want to run under windows you had better use the windows way ...