[mpich-devel] MPI_Dims_create() fails for nproc >1000000

["Antonio J. Peña"]

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 at gmail.com>
> Date: Thu, Dec 19, 2013 at 10:55 AM
> Subject: Re: [mpich-discuss] MPI_Dims_create() fails for nproc >1000000
> To: discuss at 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 at 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
>>
>>
>> --
>> ==========================================================
>> Andreas Schäfer
>> HPC and Grid Computing
>> Chair of Computer Science 3
>> Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany
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>
>
> --
> Jeff Hammond
> jeff.science at gmail.com
>
>


-- 
Antonio J. Peña
Postdoctoral Appointee
Mathematics and Computer Science Division
Argonne National Laboratory
9700 South Cass Avenue, Bldg. 240, Of. 3148
Argonne, IL 60439-4847
apenya at mcs.anl.gov
www.mcs.anl.gov/~apenya