[petsc-users] CPU-scaling

[Torquil Macdonald Sørensen]

Hi!

I'm just starting to use SLEPc on a quad-core workstation computer (Intel
Core i5-2500 CPU @ 3.30GHz).

But I'm not getting the speedup that I was expecting, when increasing the
number of cores. E.g. when running ex1.c from the documentation, on 1, 2, 3
and 4 cores. When asking for the 500 eigenvalues of smallest magnitude, for
a 5000x5000 matrix, I'm getting the following approximate timings:

# n_core  time_usage
1              480s
2              400s
3              500s
4              580s

Should I not expect a speedup for n_core > 2?

The example is using the krylovschur algorithm. For all four runs, the
program states "Number of iterations of the method: 33".

I'm using PETSc 3.4.3, SLEPc 3.4.3, OpenMPI 1.6.5, and everything is
compiled using GCC 4.8.1 or 4.8.2.

Best regards
Torquil Sørensen
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