I am looking for information on how PostgreSQL leverages or interfaces with CPU's on Linux. Does PostgreSQL let Linux do the work? Does it bypass the OS? Any information or docs you can send my way would be much appreciated.
PostgreSQL is a user land process in Linux. Linux doesn't allow itself to be bypassed by user land processes when dealing with the CPU. That is kind of its main reason for existing...
PostgreSQL uses a process forking model and each process runs on a single thread.
You can probably verify all of that by perusing the PostgreSQL documentation. Don't know what to recommend regarding Linxu, user land, kernel mode, and CPUs...