Chris Torek of UofMaryland.
I got it into 4.3-Reno. I did not come up with the whole thing but
Rehmi Post and I worked out how to compute %cpu without using floating
point (the original VAX-only version used FP but we had to stop doing
that when we were worried about porting to systems that lacked kernel
access to FP).
The version in current FreeBSD is fancier now though.
Chris