[MITgcm-devel] impldiff/solve_tridiagnonal

[Martin Losch]

Hi Jean-Michel,

I am all for it. Do you know what to do exactly or should I try to figure it out?

Martin
> On 29 Sep 2016, at 01:58, Jean-Michel Campin <jmc at mit.edu> wrote:
> 
> 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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