Imbalance in Parallel writing in ROMS -- Further Investigation Results

[koushik]

Hello All,

I have investigated the imbalance further within nf_fwrite2d.F and here are the results ---

Figure 1:

Imbalance in parallel NetCDF define phase.png (29.74 KiB) Viewed 1362 times

Figure 1: Further Parallel writing Imbalance analysis


Observations and Conclusion:
1.The imbalance is flowing as below... -- The imbalance is found in nf90_put_var calls inside nf_fwrite2d.F function during define phase.

Total CPU time ==> Output time ==> Define file ==> Wrt_Info ==> nf_fwrite2d.F ==> nf90_put_var [Further result.] [Check Figure 1]

2. nf90_put_var inside nf_fwrite2d.F during define phase calls are imbalanced and taking significant time [Check Figure 1] whereas nf90_put_var inside nf_fwrite2d.F during write phase are balanced and taking insignificant time. [Figure not included as insignificant]


3. nf90_put_var inside nf_fwrite3d.F during write phase are balanced and taking significant time. [Check Figure 2]

Figure 2.

Balance in parallel NetCDF write phase .png (13.69 KiB) Viewed 1362 times

4. With different runs with exactly same setup, the imbalance pattern is changing. -- Overshoots are happening in different PEs. [Check Figure 3]

Figure 3.

My Doubts:

1.Why nf90_put_var inside nf_fwrite2d.F is imbalanced during define phase whereas balanced during write phase although data is distributed uniformly in both cases?
2.Is there any probable reason for such imbalance? I am working on to solve such imbalance to improve the overall I/O of ROMS model.

Thanks,
Koushik Sen