OPTIONs for # threads

export OMP_NUM_THREADS=n

OPTION num_threads_pcg n

  Default: n=4
  Usually, n=4-6 is the best
  A large number creates too many I/O accesses in HDD (SSD) and slows down the PCG iterations 

OPTION num_threads_pregs n

  Default: the maximum number of threads available in your system