[MITgcm-devel] impldiff/solve_tridiagnonal

[Jean-Michel Campin]

Hi Martin,

> I could use mom/salt/tempImplVertAdv = .TRUE., right?
It's not really available, would need to change the code (change 2 or 3 "IF ()")
so that the routines that deal with implicit vertical advection
(i.e., mom_u_implicit_r.F, mom_v_implicit_r.F & gad_implicit_r.F ) 
are also called when just implicit diffusion/viscosity is turned on (even without 
implicit advection) since these routines are also doing the vertical diffusion.

Cheers,
Jean-Michel

On Wed, Sep 28, 2016 at 09:04:00PM +0200, Martin Losch wrote:
> Hi Jean-Michel,
> 
> interesting that you remember that. Yes, we have a new computer (o: So optimization starts again from scratch ???
> 
> no, I am not using CD_CODE. I could use mom/salt/tempImplVertAdv = .TRUE., right?
> 
> Martin
> 
> > On 28 Sep 2016, at 19:16, Jean-Michel Campin <jmc at mit.edu> wrote:
> > 
> > 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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> 
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