Is it because the array is already sorted? --Junchao Zhang
On Tue, Jul 2, 2019 at 12:13 PM Fande Kong via petsc-dev <[email protected]<mailto:[email protected]>> wrote: Hi Developers, John just noticed that the matrix assembly was slow when having sufficient amount of off-diagonal entries. It was not a MPI issue since I was able to reproduce the issue using two cores on my desktop, that is, "mpirun -n 2". I turned on a profiling, and 99.99% of the time was spent on PetscSortIntWithArrayPair (recursively calling). It took THREE MINUTES to get the assembly done. And then changed to use the option "-matstash_legacy" to restore the code to the old assembly routine, and the same code took ONE SECOND to get the matrix assembly done. Should write any better sorting algorithms? Fande,
