Intro
For increasing number of cores involved in compilation (e.g. Visual Studio one) you need to add the option -j to compiler (makefile) options in model configuration.
You can add a number of cores to be used e.g. -j4, but compiler can decide what amount is best if you leave it without the number and I trust it.
I assume you store your configuration as referenced, saved in a file, and use standard setup for compiler like this:
cs.set_param('BuildConfiguration', 'Faster Builds'); % Build configuration
Solution
The trick is to change build configuration so that it uses makefile option -j, my example:
cs.set_param('BuildConfiguration', 'Specify'); % Build configuration
cs.set_param('CustomToolchainOptions', {'C Compiler','-c -V$(QCC_TARGET) -g -O2 -ffast-math -fwrapv','Linker','-V$(QCC_TARGET) -g -std=gnu++14 -stdlib=libstdc++','Shared Library Linker','-V$(QCC_TARGET) -shared -Wl,--no-undefined -g','C++ Compiler','-c -V$(QCC_TARGET) -g -std=gnu++14 -stdlib=libstdc++ -O2 -ffast-math -fwrapv','C++ Linker','-V$(QCC_TARGET) -g -std=gnu++14 -stdlib=libstdc++','C++ Shared Library Linker','-V$(QCC_TARGET) -shared -Wl,--no-undefined -g','Archiver','ruvs','Make Tool','-f $(MAKEFILE) -j'}); % Toolchain details
As you can see, this is a lot, but it actually comes from the default setup, you can see it in here:
And after the change it looks like that:
So my tip is to select Build configuration to Faster Builds, then Specify, save it to file, look up for the CustomToolchainOptions and just add this -j at the end like I did. If you just copy my line it will not probably work for several reasons (used compiler, different target pc, matlab release etc.)
It should improve a bit, but only compilation time - it will not help with other parts like building model hierarchy, generating the code etc. But if your system is really big, you should get at least few minutes of improvement.