Still need the -ksp_view output. It is spending most of the time in the LU factorization and solve. I suspect the coarse problem is way to big (like you are using two levels of multigrid) and since it is solved redundantly that takes all the time. Run with say 5 levels.
Barry On Feb 23, 2012, at 3:03 PM, Francis Poulin wrote: > Hello again, > > I am using v3.1 of PETSc. > > I changed the grid sizes slightly and I'm including 4 log_summary files. > > The times are shown below. I have not modified the example at all except in > specifying the matrix size. Could it be that I need much larger? When I > tried much larger matrices I think I might have got an error because I was > using too much memory. > > n time > 2 22s > 4 29.8s > 8 33.7s > 16 28.3s > > Sorry for my first email but I hope this has more information. > > Cheers, Francis > > > <saw_log_summary_n2.txt> > <saw_log_summary_n4.txt> > <saw_log_summary_n8.txt> > <saw_log_summary_n16.txt> >> > > On 2012-02-23, at 3:27 PM, Jed Brown wrote: > >> Always send output with -log_summary for each run that you do. >> On Thu, Feb 23, 2012 at 14:16, Francis Poulin <fpoulin at uwaterloo.ca> >> wrote: >> Hello, >> >> I am learning to use PetSc but am just a notice. I have a rather basic >> question to ask and couldn't not find it on the achieves. >> >> I am wanting to test the scalability of a Multigrid solver to the 3D Poisson >> equation. I found ksp/ex22.c that seems to solve the problem that I'm >> interested in. I ran it on a large server using different processors. >> >> The syntax that I use to run using MPI was >> >> ./ex22 -da_grid_x 64 -da_grid_y 64 -da_grid_z 32 >> >> Which version of PETSc? >> >> >> I tested it using 2, 4, 8, 16 cpus and found that the time increases. See >> below. Clearly there is something that I don't understand since the time >> should be reduced. >> >> n wtime >> --------------------- >> 2 3m58s >> 4 3m54s >> 8 5m51s >> 16 7m23s >> >> Any advice would be greatly appreciated. >> >> Best regrads, >> Francis >> >> >> >
