On Tue, Aug 6, 2013 at 2:31 PM, Karl Rupp <[email protected]> wrote: > Hi Alan, > > please use -log_summary to get profiling information on the run. What is > the bottleneck? Is it the number of solver iterations increasing > significantly? If so, consider changing the preconditioner options (more > levels!). I don't expect a direct solver to be any faster in the 180k > case for a Poisson problem. >
Mudpack is geometric multigrid: http://www2.cisl.ucar.edu/resources/legacy/mudpack This should be faster. Matt > Best regards, > Karli > > > On 08/06/2013 02:22 PM, Alan wrote: > > Dear all, > > I hope you're having a nice day. > > I have a quick question on solving Poisson equation with KSP solvers > > (/src/ksp/ksp/example/tutorial/ex29.c). Currently, I run this solver > with: > > -pc_type gamg -ksp_type cg -pc_gamg_agg_nsmooths 1 -mg_levels_ksp_max_it > > 1 -mg_levels_ksp_type richardson -ksp_rtol 1.0e-7 > > It performs very well in parallel computation and scalability is fine. > > However, if I run it with a single process, the KSP solver is much > > slower than direct ones, i.e. Mudpack. Briefly, the speed difference > > between the KSP solver and the direct solver is negligible on dealing > > with small problems (i.e.36k DoFs ) but becomes very huge for moderate > > large problems (i.e. 180k DoFs). Although the direct solver inherently > > has better performance for moderate large problems in the single > > process, I wonder if any setup or approach can improve the performance > > of this KSP Poisson solver with the single process? or even make it > > obtain competitive speed (a little bit slower is fine) against direct > > solvers. > > > > thanks in advance, > > Alan > > > > -- 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
