> On Jun 22, 2018, at 5:43 AM, Pierre Jolivet <pierre.joli...@enseeiht.fr>
> wrote:
>
> Hello,
> I’m solving a system using a MATSHELL and PCGAMG.
> The MPIAIJ Mat I’m giving to GAMG has a specific structure (inherited from
> the MATSHELL) I’d like to exploit during the solution phase when the smoother
> on the finest level is doing MatMults.
>
> Is there some way to:
> 1) decouple in -log_view the time spent in the MATSHELL MatMult and in the
> smoothers MatMult
You can register a new event and then inside your MATSHELL MatMult() call
PetscLogEventBegin/End on your new event.
Note that the MatMult() like will still contain the time for your MatShell
mult so you will need to subtract it off to get the time for your non-shell
matmults.
> 2) hardwire a specific MatMult implementation for the smoother on the finest
> level
In the latest release you do MatSetOperation() to override the normal matrix
vector product with anything else you want.
>
> Thanks in advance,
> Pierre
>
> PS : here is what I have right now,
> MatMult 118 1.0 1.0740e+02 1.6 1.04e+13 1.6 1.7e+06 6.1e+05
> 0.0e+00 47100 90 98 0 47100 90 98 0 81953703
> […]
> PCSetUp 2 1.0 8.6513e+00 1.0 1.01e+09 1.7 2.6e+05 4.0e+05
> 1.8e+02 5 0 14 10 66 5 0 14 10 68 94598
> PCApply 14 1.0 8.0373e+01 1.1 9.06e+12 1.6 1.3e+06 6.0e+05
> 2.1e+01 45 87 72 78 8 45 87 72 78 8 95365211 // I’m guessing a lot of time
> here is being wasted in doing inefficient MatMults on the finest level but
> this is only speculation
>
> Same code with -pc_type none -ksp_max_it 13,
> MatMult 14 1.0 1.2936e+01 1.7 1.35e+12 1.6 2.0e+05 6.1e+05
> 0.0e+00 15100 78 93 0 15100 78 93 0 88202079
>
> The grid itself is rather simple (two levels, extremely aggressive
> coarsening),
> type is MULTIPLICATIVE, levels=2 cycles=v
> KSP Object: (mg_coarse_) 1024 MPI processes
> linear system matrix = precond matrix:
> Mat Object: 1024 MPI processes
> type: mpiaij
> rows=775, cols=775
> total: nonzeros=1793, allocated nonzeros=1793
>
> linear system matrix followed by preconditioner matrix:
> Mat Object: 1024 MPI processes
> type: shell
> rows=1369307136, cols=1369307136
> Mat Object: 1024 MPI processes
> type: mpiaij
> rows=1369307136, cols=1369307136
> total: nonzeros=19896719360, allocated nonzeros=19896719360
