[petsc-users] log_summary time ratio and flops ratio

[Jed Brown]

Xiangdong <epscodes at gmail.com> writes:

> iii) since the time ratios of VecDot (2.5) and MatMult (1.5) are still
> high, I rerun the program with ipm module. The IPM summary is here:
> https://drive.google.com/file/d/0BxEfb1tasJxhYXI0VkV0cjlLWUU/view?usp=sharing.
> From this IPM reuslts, MPI_Allreduce takes 74% of MPI time. The
> communication by task figure (1st figure in p4) in above link showed that
> it is not well-balanced. Is this related to the hardware and network (which
> the users cannot control) or can I do something on my codes to improve?

Here are a few functions that don't have any communication, but still
have significant load imbalance.

  VecAXPY          1021815 1.0 2.2148e+01 2.1 1.89e+10 1.1 0.0e+00 0.0e+00 0.0e+00  2  4  0  0  0   2  4  0  0  0 207057
  VecMAXPY          613089 1.0 1.3276e+01 2.2 2.27e+10 1.1 0.0e+00 0.0e+00 0.0e+00  1  4  0  0  0   1  4  0  0  0 414499
  MatSOR            818390 1.0 1.9608e+02 1.5 2.00e+11 1.1 0.0e+00 0.0e+00 0.0e+00 22 40  0  0  0  22 40  0  0  0 247472

You can and should improve load balance before stressing about network
costs.  This could be that the nodes aren't clean (running at different
speeds) or that the partition is not balancing data.
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