[petsc-users] testing scalability for ksp/ex22.c

[Barry Smith]

1)   Run with -ksp_view to see what solver options it is really using.  By default it is not likely using multigrid like you hope. 

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

3) Run with -log_summary to see where the time is being spent in the different cases


   Barry


On Feb 23, 2012, at 2:16 PM, Francis Poulin 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
> 
> 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
> 
>