assembly

[Thomas Geenen]

Dear Petsc users,

I would like to understand what is slowing down the assembly phase of my matrix.
I create a matrix with MatCreateMPIAIJ i make a rough guess of the
number of off diagonal entries and then use a conservative value to
make sure I do not need extra mallocs. (the number of diagonal entries
is exact)
next i call MatSetValues and MatAssemblyBegin, MatAssemblyEnd.
The first time i call MatSetValues and MatAssemblyBegin,
MatAssemblyEnd it takes about 170 seconds
the second time 0.3 seconds.
I run it on 6 cpu's and I do fill quit a number of row-entries on the
"wrong" cpu. However thats also the case the second run. I checked
that there are no additional mallocs
MatGetInfo info.mallocs=0 both after MatSetValues and after
MatAssemblyBegin, MatAssemblyEnd.

cheers
Thomas