Refer to "Spectre Circuit Simulator Reference" page 73
"... Currently, multithreading is only available for devices evaluation for BSIM3v3, and BSIM4.
Multithreading does not work with table model. If there is an instance of a primitive using table
model, multithreading would not be applied to all instances of that primitive.
Multithreading can be turned on/off by command line option, or by the multithread parameter
in the options statement from the input file. If both options are specified, command line option
will make the final determination on the number of threads to use..."