> On Feb 17, 2021, at 6:47 PM, 赵刚 <[email protected]> wrote:
>
> Dear PETSc team,
>
> I am interested in pipelined CG (-ksp_type pipecg) and Gropp's CG (-ksp_type
> groppcg), it is expected that this iterative method with pipelined has
> advantages over traditional CG in the case of multiple processes. So I'd like
> to ask for Poisson problem, how many computing nodes do I need to show the
> advantages of pipelined CG or Gropp's CG over CG (No preconditioner is used)?
>
> Currently, I can only use up to 32 nodes (36 cores per nodes) at most on my
> cluster, but both "pipecg" and "groppcg" seem to be no advantage over "cg"
> when I solve Poisson equations with homogeneous Dirichlet BC in [0, 1]^2
> (remain 20K~60K DOFs per process). I guess the reason would be too few
> computing nodes.
900 cores (assuming they are not memory bandwidth bound) might be enough to
see some differences but the differences are likely so small compared to other
parallel issues that affect performance that you see no consistently measurable
difference.
Run with -log_view three cases, no pipeline and the two pipelines and send
the output. By studying where the time is spent in the different regions of the
code with this output one may be able to say something about the pipeline
affect.
Barry
>
> Because I am calling PETSc via other numerical software, if need, I would
> mail related performance information to you by using command line options
> suggested by PETSc. Thank you.
>
>
> Thanks,
> Gang
