On multiprocessor systems, RTL synthesis leverages multiple CPU cores by default (up to eight) to speed up compile times.
The maximum number of simultaneous threads varies, depending on the number of processors available on the system, the OS, and the stage of the flow (see Vivado Design Suite User Guide: Implementation (UG904)).
The general.maxThreads Tcl parameter, a
commonality to all threads in Vivado, gives you
control to specify the number of threads to use when running RTL synthesis. For
example:
Vivado% set_param general.maxThreads <new limit>Where the <new limit> must be an integer
from 1 to 8 inclusive. For RTL synthesis, you can effectively set up to 8 threads.