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.