[petsc-users] Read in sequential, solve in parallel

[Jed Brown]

On Wed, Sep 29, 2010 at 14:34, Moinier, Pierre (UK)
<Pierre.Moinier at baesystems.com> wrote:
> Jed,
>
> Thanks for your help and thanks also to all of the others who have replied!. I made some progress and wrote a new code that runs in parallel. However the results seems to show that the time requires to solve the linear systems is the same whether I use 1, 2 or 4 processors... Surely I am missing something. I copied the code below. For info, I run the executable as: ./test -ksp_type cg -ksp_rtol 1.e-6 -pc_type none

How big is the matrix (dimensions and number of nonzeros)?  Run with
-log_summary and send the output.  This problem is mostly memory
bandwidth limited and a single core can saturate most of the memory
bus for a whole socket on most architectures.  If you are interested
in time to solution, you almost certainly want to use a
preconditioner.  Sometimes these do more work per byte so you may be
able to see more speedup without adding sockets.

Jed