Kali's John is not built with OpenMP and/or OpenCL support. The package doesn't depend on any of these libs and testing shows it does use only a single core (when not using '--fork=N` option, which is not the ideal way to run in multicore). Since almost every reasonably modern computer uses multicore CPU and has quite powerful GPU, it would be great to have the ability to exploit this extra power when cracking.

It seems JtR is already fitted for it, as stated on release notes ( http://openwall.com/lists/john-users/2014/12/18/23 )

"Due to autoconf, things such as OpenMP and OpenCL are now enabled
automatically (if system support for them is detected during build).
When this is undesirable, you may use e.g. "./configure --disable-openmp"
or "./configure --disable-openmp-for-fast-formats" and run with --fork
to achieve a higher cumulative c/s rate across the fork'ed processes."