Where "cpus" are mentioned, read "cores". I'll try to make this clearer at some point.
When Gridengine (e.g., 8.1.9) calculates cpu usage information, it is done based on slots used and either cpu time or wallclock time. This works if each slot corresponds to a single cpu. But, if more than one cpu is allocated to a slot, this calculation does not give the desired usage information.