[Users] memory address limitations, using ints?

[Erik Schnetter]

Scott

One critical number is the number of grid points per MPI process. This
number cannot exceed about 1200^3. Another critical number is the
linear size of the coarse grid multiplied by 2^(maxreflevels). This
cannot exceed about 1,000,000,000, but since this includes a 2^n term,
it can easily grow very large. Cactus and Carpet contain safeguards
that are supposed to catch any such problems. Are you building with
debug options? Those may slow down execution, but may also help find
such errors.

What is your Carpet::maxreflevels setting?

-erik

On Wed, Apr 11, 2012 at 2:12 AM, Scott Hawley <scott.hawley at belmont.edu> wrote:
> Hi.  I doing runs on Nautilus with some rather large grids, which are not
> being broken up on more than just a few (2 to 8) MPI processes.
>
> I'm noticing that there's a grid size of about 385^3 which I can't exceed,
> without Cactus/Carpet beginning to behave strangely, e.g. AHFinderDirect no
> longer works, and memory errors abound.
>
> Obviously there's the possibility that I have errors in the way I specify
> the grids in my parameter files.  But I'm wondering:
>
> Have other people had success doing "very" large runs on, say, a shared
> memory architecture where MPI /  domain decomposition are not employed?   If
> so, than I've probably just made a mistake in my par file.  If not...
>
>
> I'm wondering if this has to do with trouble address memory locations,  and
>  I notice that the type "int" is used in places, e.g. in the definition of
> CFINDEX3D,..
>
> static inline int CCTK_GFINDEX3D (const cGH *GH, int i, int j, int k);
> static inline int CCTK_GFINDEX3D (const cGH *GH, int i, int j, int k)
> {
>   return (i + GH->cctk_lsh[0]*(j + GH->cctk_lsh[1]*k));
> }
>
> Should these "int" declarations be changed to "long" or "unsigned int" in
> order to access larger numbers?
>
>
> Thanks.
>
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-- 
Erik Schnetter <schnetter at cct.lsu.edu>
http://www.perimeterinstitute.ca/personal/eschnetter/