[petsc-users] Code speedup after upgrading

[Mohammad Gohardoust]

Thanks Lawrence for your suggestion. It did work and the BuildTwoSided time
is almost zero now:

BuildTwoSided 4 1.0 1.6279e-0310.1 0.00e+00 0.0 2.0e+02 4.0e+00 4.0e+00
BuildTwoSidedF 3 1.0 1.5969e-0310.5 0.00e+00 0.0 2.0e+02 3.6e+03 3.0e+00

Mohammad

On Thu, Mar 25, 2021 at 4:54 AM Lawrence Mitchell <wence at gmx.li> wrote:

>
>
> > On 24 Mar 2021, at 01:30, Matthew Knepley <knepley at gmail.com> wrote:
> >
> > This is true, but all the PETSc operations are speeding up by a factor
> 2x. It is hard to believe these were run on the same machine.
> > For example, VecScale speeds up!?!  So it is not network, or
> optimizations. I cannot explain this.
> >
>
> VecMDot speeds up by a factor of 8!
>
> Unrelatedly, one thing I see, which _may_ offer potential for much more
> speedup, is this:
>
> BuildTwoSided      17548 1.0 4.9331e+00 9.9 0.00e+00 0.0 5.9e+05 4.0e+00
> 1.8e+04
> BuildTwoSidedF     17547 1.0 5.0489e+00 7.3 0.00e+00 0.0 1.2e+06 3.6e+03
> 1.8e+04
>
> ...
>
> MatAssemblyBegin   17547 1.0 8.8252e+00 1.1 0.00e+00 0.0 1.2e+06 3.6e+03
> 1.8e+04
> MatAssemblyEnd     17547 1.0 2.6903e+00 2.8 2.79e+07 2.7 2.1e+02 2.0e+02
> 1.0e+01
>
> I think these BuildTwoSided calls are coming from the MatAssemblyBegin/End
> pairs.
>
> If you preallocate and fill your matrices with zeros in all the possible
> places that you might end up putting a non-zero, then calling
>
> MatSetOption(mat, MAT_SUBSET_OFF_PROC_ENTRIES, PETSC_TRUE)
>
> on the matrix you create will reduce this time in BuildTwoSided to almost
> zero.
>
> Lawrence
>
>
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