[petsc-users] Poisson equation with CG and BoomerAMG

[Barry Smith]

  http://www.mcs.anl.gov/petsc/documentation/faq.html#computers

likely you will not benefit from using more than 4 or at most 6 cores at of the 8 for each node. This is a memory hardware limitation.

   Barry

On Jul 10, 2012, at 8:22 AM, Benjamin Sanderse wrote:

> Hello all,
> 
> I am solving a Poisson equation with Neumann BC on a structured grid (arising from an incompressible Navier-Stokes problem). Although my mesh is structured, the matrix is 'given' so I am using AMG instead of geometric multigrid, for the moment.
> To solve the Poisson equation I use CG with preconditioning provided by BoomerAMG, using standard options. I have run my problem for different grid sizes and number of processors, but I am confused regarding the parallel scalability. Attached are some timing results that give the average time spent on solving the Poisson equation. As you can see, when going from 1 to 2 processors, the scaling is very good, even for the case of 200^3 grid points (8 million). For larger number of processors this quickly deteriorates. The cluster I am running on has 8 cores per node and 24GB memory per node. 
> Can someone comment on these results? Is this what I should expect?
> 
> Some additional information:
> - I set the NullSpace of the matrix explicitly with MatNullSpaceCreate
> - The set-up of the problem is not included in the timing results. The set-up is not efficient yet (use of MatRow, for example), and there is some code cleanup to do (too many matrices and vectors), but I think this should not affect the performance of the Poisson solve.
> - log_summary and ksp_monitor are attached. 
> 
> Thanks a lot,
> 
> Benjamin
> 
> <log_summary>
> <timing>
> <ksp_view>
> 
> 
> 
> -- 
> Ir. B. Sanderse
> 
> Centrum Wiskunde en Informatica
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> 
> t: +31 20 592 4161
> e: sanderse at cwi.nl
>