Florian Lindner <[email protected]> writes: > I'm more or less aware of that, but I'm surprised that the performance is > such poor.
If you've ever written a naive triply-nested loop dgemm, you'd know that it gives up orders of magnitude. > I changed the format of matrixC to dense now, but the runtime is still poor. > Overall time is now around 9s with 95% spent in KSPSolve and exact the same > number of MatMult executions, taking 65% of time. Your solver is broken. It takes 10000 iterations and presumably returns KSP_DIVERGED_ITS (use -ksp_converged_reason to check). This could be due to GMRES restarts. You might have better results with -ksp_type cg (if your matrix is symmetric) or -ksp_type bcgs for nonsymmetric. But the bottom line is that you need a good preconditioner (or well-conditioned system) for iterative methods to make sense for dense matrices.
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