There are plenty of posts about this already:
How well does Source 2 use multiple CPU cores? For me, GMOD feels like it always only uses one core for literally everything, which at least makes coding stuff easier.
Now with CPUs that actually have 128 logical cores, servers could extremely benefit from physics and entity logic being handled in seperate threads.
Is this even possible and does Source 2 already do that and with what extent?
Is there a plan for allowing user-created scripts to use multiple threads?
How would it work? Any limitations? Any other thoughts?
And from garry themselves:
Like Source 1, a bunch of processes are spread over multicore. But you’re only going to get all your cores being used it if has to do a lot of those.
For example, if the animation/bone system is multithreaded, that means that it’s going to take each model and split them into stacks for each worker thread to work through. If you only have one animated model in your scene it isn’t really gonna be of any benefit.
It should be noted; that the performance improvements over gmod with multithreading will likely be due to addon developers being able to use multiple threads. As such, it is up to addon developers to actually make use of them.