Lets say I have a code like this
start = MPI_Wtime()
<Run the solver>
stop = MPI_Wtime();
What happens when right after start=MPI_Wtime(), the timeslice of the process ( from the operating system's perspective not the MPI process) is over, and the operating system schedules a next process, after saving the context switch, and eventually this application would resume, once its process is scheduled back by the os.
Does MPI_Wtime() takes care of storing/updating the time when this happens?
Of course, part of the answer lies in the implementation of Wtime.