To test the parallel efficiency, the surface evolution was calculated for a sphere expanding at constant speed. The calculation was performed using 1, 2, 4, 8, and 16 cores of AMD Opteron 8435 processors clocking at . The corresponding average calculation times for a single time step and for different sphere diameters (measured in grid spacings) are listed together with the parallel efficiency in Table 4.4.

According to Amdahl's law [9] the parallel efficiency decreases with the number of CPUs due to sequentially processed parts of the program. In case of 16 cores a parallel efficiency of approximately could be achieved except for the smallest sphere diameter . For smaller structures the overhead due to thread synchronization is more relevant, which results in a worse efficiency. Table 4.4 also shows the good scalability with surface size. If the diameter is multiplied by 10, the surface of the sphere is increased by a factor of 100, which is well reproduced by the listed runtimes.

Otmar Ertl: Numerical Methods for Topography Simulation