Interesting! What do you mean with dof blocking?
So it looks like the SCOTCH reordering is faster to build but performs similar to the old Boost reordering? Johan On Mon, Sep 16, 2013 at 2:32 PM, Garth N. Wells <gn...@cam.ac.uk> wrote: > Here are some quick numbers for anyone interested in the impact of dof > re-ordering, and why DOLFIN renumbers the UFC dofmap by default. For a > vector-valued reaction-diffusion problem using P2 Lagrange elements in > 3D (6.44M dofs) and PETSc as the backend: > > Ordering method | None | Random* | A* | A | B* | B > > ----------------------------|-------|---------|-------|-------|-------|------- > Call graph ordering | 0.0s | - | 1.2s | 9.2s | 2.4s | > 17.87 > Assembly | 27.9s | 34.4s | 29.3s | 29.4s | 30.2s | 32s > 100 CG + Jacobi iterations | 221s | 1177s | 142s | 176s | 140s | > 160s > > > A: New SCOTCH reordering (Gibbs-Poole-Stockmeyer) > B: Boost reordering (reverse Cuthill-McKee) > *: With dof blocking > > The Krylov solver speed-up with re-ordering and dof blocking is > dramatic. Speed-ups are also observed when using direct solvers, but > these are less dramatic. The small drop in assembly when the dofs are > re-ordered is due to reduced memory locality in the linear algebra > objects with respect to the order in which the mesh cells are iterated > over. This can be (and soon will be) fixed by re-ordering the mesh > indices. It has been observed that some solvers (e.g. BommerAMG fail > to converge for this problem without re-ordering, and converge in <10 > iterations with re-ordering and dof blocking). > > The DOLFIN UnitFooMesh ordering is quite cache-friendly. Meshes > created by 3rd-party libraries are unlikely to be as cache-friendly > and could tend towards the random ordering timing, > > Garth > _______________________________________________ > fenics mailing list > fenics@fenicsproject.org > http://fenicsproject.org/mailman/listinfo/fenics >
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