I noticed several 64-bit divides for HZ/USER_HZ, and also the fact that 
HZ == USER_HZ on many architectures (or if you play with scaling it ;).  
Since do_div is macroized to optimized assembler on many platforms, we 
emit long divides for divide by one.  This could be extended further to 
recognize other power of two divides, but I don't think the complexity 
of the macros would be justified.  I also didn't feel it was worthwhile 
to optimize this for non-constant divides; if you feel otherwise, please 
extend.

Cheers,

Zachary Amsden
zach@vmware.com