[MITgcm-devel] impldiff/solve_tridiagnonal

[Jean-Michel Campin]

Hi Martin,

I found an email on the list iwith an interesting Post-Scriptum that was arguing 
in the other direction, i.e., to allow NOT to use SOLVE_DIAGONAL_KINNER code:
http://mitgcm.org/pipermail/mitgcm-devel/2011-October/004995.html

But appart from that (and I agree that this performance issue is platform/compiler 
dependent), I thought we could try not to use impldiff.F anymore (most of the code 
is there except for CD_CODE) and leave impldiff.F to the retirement track.
Are you using the CD_CODE ?

Cheers,
Jean-Michel

On Wed, Sep 28, 2016 at 06:41:07PM +0200, Martin Losch wrote:
> Hi there,
> 
> impldiff.F turns out to be one of the expensive routines on some platforms. One of the reasons is apparently poor cache efficiency. In solve_tridiagonal this is ???solved??? by moving the k-loop inside the i,j loops. There???s a CPP flag SOLVE_DIAGONAL_KINNER to turn that on in solve_tridiagonal.
> 
> Would anyone object to me implementing something like this in impldiff.F? I would use SOLVE_DIAGONAL_KINNER (off by default) to turn this feature on.
> 
> Martin
> 
> PS. would be much better if impldiff would actually call solve_tridiagonal, right?
> 
> 
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