[petsc-users] Not getting scalability.

[Gaurish Telang]

Oh thank you, this was helpful.  I am interested in iterative solvers, so
what is the minimum matrix size you
think that strong scalability will show up for such methods?












On Mon, Mar 7, 2011 at 9:38 AM, Matthew Knepley <knepley at gmail.com> wrote:

> On Mon, Mar 7, 2011 at 8:20 AM, Gaurish Telang <gaurish108 at gmail.com>wrote:
>
>> Hi,
>>
>> I have been testing PETSc's scalability on clusters for matrices of sizes
>> 2000, 10,000, uptill 60,000.
>>
>
> 1) These matrices are incredibly small. We usually recommend 10,000
> unknowns/process for weak scaling. You
>     might get some benefit from a shared memory implementation on a
> multicore.
>
>
>> All I did was try to solve Ax=b for these matrices. I found that the
>> solution time dips if I use upto 16 or 32 processors. However for a larger
>> number of processors however the solution time seems to go up rather than
>> down. IS there anyway I can make my code strongly scalable ?
>>
>
> 2) These are small enough that direct factorization should be the fastest
> alternative. I would try UMFPack, SuperLU, and MUMPS.
>
>     Matt
>
>
>> I am measuring the total time (sec) and KSP_SOLVE time in the -log_summary
>> output. Both times show the same behaviour described above.
>>
>> Gaurish
>>
> --
> 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
>
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