[petsc-users] Bad memory scaling with PETSc 3.10

[Mark Adams]

GAMG look fine here but the convergence rate looks terrible, like 4k+
iterations. You have 4 degrees of freedom per vertex. What equations and
discretization are you using?

Your eigen estimates are a little high, but not crazy. I assume this system
is not symmetric.

AMG is oriented toward the laplacian (and elasticity). It looks like you
are solving Stokes. AMG will not work on the whole system out of the box.
You can use it for a 3 dof velocity solve in a FieldSolit solver




On Mon, Mar 11, 2019 at 6:32 AM Myriam Peyrounette <
myriam.peyrounette at idris.fr> wrote:

> Hi,
>
> good point, I changed the 3.10 version so that it is configured with
> --with-debugging=0. You'll find attached the output of the new LogView. The
> execution time is reduced (although still not as good as 3.6) but I can't
> see any improvement with regard to memory.
>
> You'll also find attached the grep GAMG on -info outputs for both
> versions. There are slight differences in grid dimensions or nnz values,
> but is it significant?
>
> Thanks,
>
> Myriam
>
>
>
> Le 03/08/19 à 23:23, Mark Adams a écrit :
>
> Just seeing this now. It is hard to imagine how bad GAMG could be on a
> coarse grid, but you can run with -info and grep on GAMG and send that. You
> will see listing of levels, number of equations and number of non-zeros
> (nnz). You can send that and I can get some sense of GAMG is going nuts.
>
> Mark
>
> On Fri, Mar 8, 2019 at 11:56 AM Jed Brown via petsc-users <
> petsc-users at mcs.anl.gov> wrote:
>
>> It may not address the memory issue, but can you build 3.10 with the
>> same options you used for 3.6?  It is currently a debugging build:
>>
>>               ##########################################################
>>               #                                                        #
>>               #                       WARNING!!!                       #
>>               #                                                        #
>>               #   This code was compiled with a debugging option.      #
>>               #   To get timing results run ./configure                #
>>               #   using --with-debugging=no, the performance will      #
>>               #   be generally two or three times faster.              #
>>               #                                                        #
>>               ##########################################################
>>
>>
> --
> Myriam Peyrounette
> CNRS/IDRIS - HLST
> --
>
>
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