Problem
An executable build with:
module load intel/19.0.3 impi/2019.3
is up to 20% slower than an executable build with identical code and optimisation, compared with
module load intel/18.0.5 impi/2018.4
Mostly affects code pieces are dominated by communication, but also serial code is affected.
Solution
Stay, if possoble, with the compiler/mpi version 18.
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