[petsc-users] Strange strong scaling result

[Ce Qin]

Dear all,

I want to analyze the strong scaling of our in-house FEM code.
The test problem has about 20M DoFs. I ran the problem using
various settings. The speedups for the assembly and solving
procedures are as follows:
                                   Assembly     Solving
NProcessors NNodes CoresPerNode
1           1      1                    1.0         1.0
2           1      2               1.995246    1.898756
            2      1               2.121401    2.436149
4           1      4               4.658187    6.004539
            2      2               4.666667    5.942085
            4      1                4.65272    6.101214
8           2      4               9.380985   16.581135
            4      2               9.308575   17.258891
            8      1               9.314449   17.380612
16          2      8              18.575953   34.483058
            4      4              18.745129   34.854409
            8      2              18.828393    36.45509
32          4      8              37.140626   70.175879
            8      4              37.166421   71.533865

I don't quite understand this result. Why we can achieve a speedup of
about 70+ using 32 processors? Could you please help me explain this?

Thank you in advance.

Best,
Ce
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