100% CPU Utilization Using 10ms Periodic Task

[Phalanx]

Here's what I'm doing. In the 10ms loop in Periodic Tasks I have the following:

2 separate GET digital I/O VI's
Each output I perform a Boolean NOT
Each output is stored in a Boolean global variable.
The RefnumGet VI's are outside the loop.

When this code is added, my CRIO cpu spikes to 100%.
When I remove this code my CRIO CPU is at 50%.

I'm rather puzzled/stumped that this little bit of code causes that much pain.
Any ideas?