On multiprocessor systems, RTL synthesis leverages multiple CPU cores by default (up to four) 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, which is
common 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, 4 is the maximum number of threads that can be set effectively.