The MPI Serialisation Efficiency (MPI SerE) describes any loss of efficiency due to dependencies between processes causing alternating processes to wait.
It is expressed as:
\[MPI\_SerE = \frac{Max(OutMPI_{1,1}, \cdots, OutMPI_{P,1})}{IdealRuntime}\]In order to fully understand the formulas, you may also visit the glossary of the metrics terms.