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.
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 >
