Why doesn't increasing the number of threads help?

Question

Multithreading

In a nutshell, the new version of the cloud platform is based on kubernetes. Services have controllers (reconcilers) for each type of object. My task is to increase the number of concurrent reconciles per controller to increase performance.
I built and ran a sea of ​​gatling simulations of our user scripts, configuring different numbers of threads for the controller. As a result, there is practically no difference in response times. That is, an increase in the number of threads does not give a result ...
In a 4 cores system , the
question is: what to do? Why isn't there a tendency to speed up as the number of threads increases? How then to increase the performance of the system?

Answer 1

The system has 4 cores

Well, you have four cores, which means physically more than four different operations cannot occur simultaneously.
So it makes no sense to create more than 4 threads.

Answer 2

Services have controllers (reconcilers) for each type of object. My task is to increase the number of concurrent reconciles per controller to increase performance.

Are you sure you mean the K8S controllers and not the number of pods?
What else is in the system? Database? Queue?