What about a mixed approach? If we've received no complaints so far that means that the current LUT is fine in most cases. We could fall into runtime computations if it's larger that that value. That will introduce a forced check, but the overhead will be lower than always computing, while the memory consumption would keep the same and the values not limited.

 Toni


On 12/19/2013 11:13 AM, Jeff Hammond wrote:

I started working on a patch, but I'm not sure if it is the right

thing to just encode a longer static array of primes.

Any suggestions on how to proceed?  Should I generate the array of

primes on-the-fly (once per MPI instance) up to the max possible

amount?

Jeff

---------- Forwarded message ----------

From: Jeff Hammond <jeff.science@gmail.com>

Date: Thu, Dec 19, 2013 at 10:55 AM

Subject: Re: [mpich-discuss] MPI_Dims_create() fails for nproc >1000000

To: discuss@mpich.org

Can you provide a short test that reproduces the issue you are seeing?

 I will add a Trac ticket for it.

Thanks,

Jeff

On Thu, Dec 19, 2013 at 9:49 AM, Andreas Schäfer <gentryx@gmx.de> wrote:

Hi,

I noticed that MPICH's MPI_Dims_create() fails with a floating point

exception, if the number of processes is larger than 10^6. Apparently

the reason is that the prime factors are hard coded into the code and

are limited to 1000 (or sqrt(10^6)). Open MPI's implementation has no

such limitation.

Best

-Andreas

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