[MITgcm-support] Something very slow has happened to the pressuresolver

[Christopher L. Wolfe]

> Christopher, I am no expert on solve_for_pressure but first thing I  
> would look at is the number of cg2d_iters that it does.  Set  
> ALLOW_DEBUG and debuglevel=1

I'll check it, but should the number be different for two runs  
differing only by the code itself?

Christopher

On Feb 27, 2008, at 3:59 AM, Dimitris Menemenlis wrote:

> Christopher, I am no expert on solve_for_pressure but first thing I  
> would look at is the number of cg2d_iters that it does.  Set  
> ALLOW_DEBUG and debuglevel=1
>
> -----Original Message-----
>
> From:  "Christopher L. Wolfe" <clwolfe at ucsd.edu>
> Subj:  [MITgcm-support] Something very slow has happened to the  
> pressuresolver
> Date:  Wed Feb 27, 2008 2:04 am
> Size:  2K
> To:  mitgcm-support at mitgcm.org
>
>
> Hello modelers,
>
> I ran MITgcm on a Cray X1E (Phoenix at ORNL) about a year ago with  
> good results. I recently got more time on this machine and  
> downloaded the latest MITgcm checkpoint (59n), but was dismayed to  
> find that this checkpoint is A LOT (like 5x) slower than the one I  
> was originally using (58q_post). I ran freshly compiled versions of  
> checkpoint_58q_post and checkpoint_59n with identical model  
> configurations, compiler options, and CPP options (to the extent  
> possible) and discovered that the pressure solver in 59n takes ten  
> times (!) more CPU time on the X1E than the pressure solver from  
> 58q_post. No other routine seems to haveacquiredmore than about 10%  
> greater overhead. Interestingly, I have not noticed significant  
> increases in the pressure solver overhead on IBM sp4 machines.
>
>
> Before I start a flurry of diffs, does anyone have any idea what has  
> has been done to the pressure solver over the past year that would  
> have had such a significant impact on its performance on the Cray?
>
> Thanks in advance,
> Christopher
>
> -----------------------------------------------------------
>
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