2007/8/27, Anders Logg <logg@xxxxxxxxx>:
Martin Sandve Alnæs wrote:
2007/8/27, Anders Logg <logg@xxxxxxxxx>:
3. It should be relatively easy to extend the current assembler in
src/kernel/fem/Assembler.cpp to do parallel assembly. It currently knows
how to assemble over subdomains (defined by some MeshFunctions) and the
parallel assembly would be similar: skip the cells (if (.. != ... )
continue;) that don't belong to the current processor.
It should rather iterate over cells that _are_ on the current
processor. Even if the mesh isn't distributed yet, this is probably
important.
Why is it important? Iterating over all cells and skipping is very cheap
(I imagine). Doing ++cell_iterator in DOLFIN only increases an int
counter (inline). It probably takes more time to preprocess and extract
the list of cells belonging to the process.
Because it's O(N_global), and needs to be O(N_local) to scale with
increased parallelism. I guess it's cheap enough for small scale
paralellism, but if you run with 100 subdomains (processes), then
that's 100 ++cell_iterator for each cell in the local mesh. So it is
fine until the mesh itself is distributed.
