System calls overhead

Question

I just started studying about system calls. I would like to know what causes overhead when a system call is made.

For example, if we consider getpid(), when a system call is made to getpid() my guess is that if the control is currently in the child process then a context switching has to be made to enter the parent process to get the pid. Can that contribute to overhead?

Also when getpid() is called, there will be some metadata transfer across the user-space boundary and enters and exits the kernel.So will the constant switching between user space and kernel also cause some overhead?