There are many papers published at this subject. Google scholar with a search for "system noise" will give you a starting point.
On Dec 7, 2009, at 10:13 , Douglas Guptill wrote:
>> In most MPI applications if even one task is sharing its CPU with
>> other processes, like users doing compiles, the whole job slows down
>> too much.
> I have not found that to be the case.