Doing simple floating point or integer arithmetic is limited since if another execution core is not busy, the system will (presumably?) assign CPU resources to where they are needed so I could be getting the performance of 2 or more cores theoretically?
Any good reliable way to benchmark this on IBM Hardware?
For example, some older Power systems come rated with higher MHz rates but I want to see that advantage, if applicable, in a simple test. Anyway to do this through the CLI without having to install anything new or big?
Assuming you are writing your own software, no, you have to actually program the so called thread allocation yourself.
Making an even bigger assumption that you are using C++, it is probably easiest to work with a library such as Boost or Intel TBB.
You can use the command top to see what your processes are doing.
Multithreading does not work that way; two cores can't cooperate to run a single-threaded program faster. Single-threaded programs will run slower on machines with lots of slower cores; we've had some puzzled folks ask us why their new machines have worse single-threaded benchmarks than their old ones.
But more cores means you can run more threads or processes at once without sharing time; more total work can be accomplished in the aggregate; but a program has to be designed with this in mind (or multiple instances of it run) to take advantage of this capability.