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 > Science Park 123 > 1098 XG Amsterdam > > t: +31 20 592 4161 > e: sanderse at cwi.nl >
