Slow speed after changing from serial to parallel

[Matthew Knepley]

1) There is no way to have any idea what is going on in your code
    without -log_summary output

2) Looking at that output, look at the percentage taken by the solver
    KSPSolve event. I suspect it is not the biggest component, because
   it is very scalable.

   Matt

On Sun, Apr 13, 2008 at 4:12 AM, Ben Tay <zonexo at gmail.com> wrote:
>
>
> Hi,
>
> I've a serial 2D CFD code. As my grid size requirement increases, the
> simulation takes longer. Also, memory requirement becomes a problem. Grid
> size 've reached 1200x1200. Going higher is not possible due to memory
> problem.
>
> I tried to convert my code to a parallel one, following the examples given.
> I also need to restructure parts of my code to enable parallel looping. I
> 1st changed the PETSc solver to be parallel enabled and then I restructured
> parts of my code. I proceed on as longer as the answer for a simple test
> case is correct. I thought it's not really possible to do any speed testing
> since the code is not fully parallelized yet. When I finished during most of
> the conversion, I found that in the actual run that it is much slower,
> although the answer is correct.
>
> So what is the remedy now? I wonder what I should do to check what's wrong.
> Must I restart everything again? Btw, my grid size is 1200x1200. I believed
> it should be suitable for parallel run of 4 processors? Is that so?
>
> Thank you.



-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which
their experiments lead.
-- Norbert Wiener