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

[Barry Smith]

  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
>> 
>> 
>> 
>