So it means we will be getting better performance if we are implementing multithreading in a servlet.
Again, I'm not sure what you mean by "implement multithreading". Servlets
are multi-threaded, unless you take the specific step I mentioned before. The servlet developer of course has to make the servlet code thread-safe, but it's multi-threaded regardless of thread-safety.
The multi-threaded operation of servlets has nothing to do with creating Threads objects in the servlet code, in case that's what you're wondering about.
people never prefer to implement multithreading in a servlet.
I don't know where you got this idea. Multithreading is essential for web sites where performance is a factor (which means just about all of them).
But since you seem to use "implement multithreading" in an incorrect way, maybe you can make it clearer what you mean by this statement.