[Mitgcm-support] First and PRELIMINARY findings with new code

[mitgcm-support at dev.mitgcm.org]

Carl, John, Alistair and Chris;

Patrick is on its way back to the east coast and he will report more on this 
matter once he is back. We made progress here which allowed us not to start 
parallel experiments with both codes. Quite obviously there are still interfaces 
missing related to the optimization. 

But the important thing is that we started to compare timings, storage 
requirements, etc between the old and the new code. In some sense the numbers we 
have so fare are preliminary and we will continue along those lines. However, 
the findings we have by now are somewhat alarming and frustrating. Our numbers 
are still preliminary but I think the following is worth some warning:

1) The old code runs on the Origing 2000 with automatic parallelization about as 
efficient as the new code - this is true on 12 CPUs and for a 2 degree model. 
Results could look different with more CPUs and/or higher resolution.

2) The new code requires at least 5 times more core memory through a 
substantially higher storage requirement. Patrick suggested that he can reduce 
that by some fraction. But the primary differences could reside in the different 
time stepping schemes that create different dependencies. I will ask Ralf to 
check carefully all the store directives implemented right now. Several might 
not be required as a recomputation could be much more efficient - if it is 
small. Pending further confirmation - as the code stands right now we could not 
do the computations I am doing with the classic code since we could not effort 
the storage.

For more details I refer to Patrick's verbal report. 

Detlef.

-- 
Detlef Stammer

Physical Oceanography Research Division
Scripps Institution of Oceanography
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