[MITgcm-support] optimization: lapack? flags?

[Martin Losch]

Hi Andrea,

Micheal is right about the optimization. The flags useSingleCpuIO and globalFiles only change the I/O, which can also depend on the machine that you are working on. True code optimization has to be done with compiler flags (in the build options file), or if you can spot something seriously inefficient, directly in the code.

I think you always get an “No” on LAPACK because this test is never done in genmake2. I am not aware of any forward code that uses Lapack. I think some of the very specialized adjoint applications use Lapack for singular value decompositions.

Martin

> On 5 Apr 2017, at 16:13, Michael Schaferkotter <schaferk at bellsouth.net> wrote:
> 
> A.
> 
> Optimization choices are machine dependent.
> 
> Your intended audience would need to know the machine architecture that you are targeting.
> 
> Please provide.
> 
> michael
> 
> Sent from my iPhone
> 
>> On Apr 5, 2017, at 07:42, Andrea Cimatoribus <andrea.cimatoribus at epfl.ch> wrote:
>> 
>> Dear all,
>> I am starting to do some more ambitious simulations, in terms of computational effort, and it is thus time for me to optimize the compilation a bit. I know it is mostly a matter of trial and error with compiler options, but I would like to ask you if you have some suggestion on two specific points:
>> 
>> - Is it possible to compile using gfortran and use intel MKL? My genmake2 now reports that it is compiling without LAPACK. I tried to link to the Intel MKL I have on my machine (while still using gfortran, we don't have intel compilers for the moment), but without much success. Is anyone actually using LAPACK? Does it make a difference? I could find hardly anything in the archives.
>> - Apart from the "classical" useSingleCpuIO and globalFiles, is there any other runtime flag which has a significant impact on execution time (but does not affect the results)?
>> 
>> Thank you very much, Andrea
>> 
>> -- 
>> Andrea Cimatoribus
>> postdoctoral researcher
>> EPFL ENAC IIE ECOL
>> https://people.epfl.ch/andrea.cimatoribus
>> 
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