[petsc-users] Software for load balancing to improve parallel performance to be used with PETSc

[Jed Brown]

On Mon, Jan 9, 2012 at 09:57, TAY wee-beng <zonexo at gmail.com> wrote:

> I only compute rows which the processor own. Can it be the memory
> allocation? I'll check on that.
>

Usually memory allocation mistakes cost much more.


>
>  Most of your solve time is going into PCSetUp() and PCApply, both of
> which are getting more expensive as you add processes. These are more than
> 10x more than spent in MatMult() and MatMult() takes slightly less time on
> more processes, so the increase isn't entirely due to memory issues.
>
>  What methods are you using?
>
>
> What do you mean methods? I am doing Cartesian grid 3d CFD,
>

Then just use a regular partition. If your meshes have boundary layers, you
might want to adjust the subdomain aspect ratios so that strongly coupled
cells tend to reside on the same process, but don't bother with general
graph partitions (like ParMETIS) because you will end up writing most of an
unstructured CFD code in order to use those partitions efficiently.


> using fractional mtd which solves the momentum and Poisson eqns. I
> construct the linear eqn matrix and insert them in PETSc matrix/vectors.
> Then I solve using Bicsstab and hypre AMG respectively. Why is PCSetUp()
> and PCApply using more time?
>

It is expensive because BoomerAMG setup and apply is expensive.
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