[dune-pdelab] Scalability issue in overlapping solvers

[Aswin vs]

Dear Sir,
Thank you for your response. I have used the following values in the
problem:

dim = 2
Domain = [0,1]^2
dt = 0.0075
Final time = 2dt
degree = 1
cells = {500, 500} and global Refine = 1
overlap = 1

ISTLBackend_OVLP_BCGS_ILU0 is used as the linear solver.

I am  using a system with Intel Core™ i7-10700 CPU @ 2.90GHz × 1 processor,
that has 8/16 number of cores/threads
*.*

On Mon, Jan 3, 2022 at 10:18 PM Peter Bastian <
Peter.Bastian at iwr.uni-heidelberg.de> wrote:

> Hello Aswin,
>
> maybe you could give us a bit more information, e.g.
>
> - problem size ? and overlap size
> - seems to be an inexact subdomain solver?
> - what machine did you use? How many cores/nodes ?
>
> Best,
>
> Peter
>
> Am 03.01.22 um 11:09 schrieb Aswin vs:
>
> Hello,
>
> Can somebody suggest me how to get good scalability while using the
> overlapping solvers in DUNE. I tried the following test example in DUNE
> PDELab, but not getting good scalability.
> Thank you.
>
> $  mpirun -np 1 ./test-heat-instationary-periodic
> .
> .
> .
> STAGE 2 time (to):   1.5000e-02.
> === matrix setup skipped (matrix already allocated)
> === matrix assembly (max) 0.9944 s
> === residual assembly (max) 0.4861 s
> === solving (reduction: 1e-10) === Dune::BiCGSTABSolver
> === rate=0.8397, T=12.57, TIT=0.09524, IT=132
> 12.68 s
> ::: timesteps           2 (2)
> ::: nl iterations     565 (565)
> ::: lin iterations    565 (565)
> ::: assemble time    8.0477e+00 (8.0477e+00)
> ::: lin solve time   5.3414e+01 (5.3414e+01)
>
> ---------------------------------------------------------------------------------------
> $ mpirun -np 2 ./testheat-instationary-periodic
> .
> .
> .
> STAGE 2 time (to):   1.5000e-02.
> === matrix setup skipped (matrix already allocated)
> === matrix assembly (max) 0.5053 s
> === residual assembly (max) 0.2465 s
> === solving (reduction: 1e-10) === Dune::BiCGSTABSolver
> === rate=0.9268, T=26.95, TIT=0.08895, IT=303
> 27.05 s
> ::: timesteps           2 (2)
> ::: nl iterations    1254 (1254)
> ::: lin iterations   1254 (1254)
> ::: assemble time    4.0910e+00 (4.0910e+00)
> ::: lin solve time   1.1201e+02 (1.1201e+02)
>
> ---------------------------------------------------------------------------------------
> $ mpirun -np 4 ./testheat-instationary-periodic
> .
> .
> .
> STAGE 2 time (to):   1.5000e-02.
> === matrix setup skipped (matrix already allocated)
> === matrix assembly (max) 0.271 s
> === residual assembly (max) 0.1318 s
> === solving (reduction: 1e-10) === Dune::BiCGSTABSolver
> === rate=0.9232, T=26.02, TIT=0.0894, IT=291
> 26.11 s
> ::: timesteps           2 (2)
> ::: nl iterations    1249 (1249)
> ::: lin iterations   1249 (1249)
> ::: assemble time    2.1746e+00 (2.1746e+00)
> ::: lin solve time   1.1165e+02 (1.1165e+02)
>
> ---------------------------------------------------------------------------------------
> $ mpirun -np 8 ./testheat-instationary-periodic
> .
> .
> .
> STAGE 2 time (to):   1.5000e-02.
> === matrix setup skipped (matrix already allocated)
> === matrix assembly (max) 0.1772 s
> === residual assembly (max) 0.08259 s
> === solving (reduction: 1e-10) === Dune::BiCGSTABSolver
> === rate=0.9288, T=30.81, TIT=0.09751, IT=316
> 30.89 s
> ::: timesteps           2 (2)
> ::: nl iterations    1329 (1329)
> ::: lin iterations   1329 (1329)
> ::: assemble time    1.3485e+00 (1.3485e+00)
> ::: lin solve time   1.2796e+02 (1.2796e+02)
>
>
> --
> Aswin V.S.
> Research Associate-I
> School of Mathematics
> *Indian Institute of Science Education and Research Thiruvananthapuram*
> Contact: +91 8089542946 / 7994312946
> *_____________________________________*
> "The secret of life is not enjoyment but education through experience."
> ― Swami Vivekananda
>
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