Why doesn't the OS use all my CPU?

[declan]

I'm running a fairly resource intensive program. My machine has two processors. It runs Mac OS X. My program is doing multiprocessing using OpenMP. If I look in top/htop, it IS using more than 100%, but it is usually around 130%. If I add up the top few numbers, the sum is nowhere near 200%. Why doesn't my program use the rest? Or is the rest being used implicitly somewhere?

Thanks!

[Athar]

Without knowing the program in question, one can still at least say that the threads are waiting for something part of the time - most likely for a lock to be freed or for I/O operations to complete.

[bigearsbilly]

any process using 100% of total cpu is usually a sign of trouble.

remember the OS is working away underneath, daemons, services, the screen needs to be drawn,
disks handled, memory shuffled about
etc.

[declan]

Ok, but that's what I'm saying. I know the OS needs a bunch of CPU. But that would show up in top as Xorg, or HAL, or DBUS, or whatever. But the SUM of all the things doesn't add up to 200%.