On Mon, Mar 7, 2011 at 8:43 AM, Gaurish Telang <gaurish108 at gmail.com> wrote:
> Oh thank you, this was helpful. I am interested in iterative solvers, so > what is the minimum matrix size you > think that strong scalability will show up for such methods? > Such blanket predictions are not worth much for strong scaling since they depend on the architecture, interconnect, etc. What is most important is to understand the timing output in -log_summary and see what is not scaling correctly. Dave pointed out that linear iterations must also scale correctly. Matt > > On Mon, Mar 7, 2011 at 9:38 AM, Matthew Knepley <knepley at gmail.com> wrote: > >> On Mon, Mar 7, 2011 at 8:20 AM, Gaurish Telang <gaurish108 at >> gmail.com>wrote: >> >>> Hi, >>> >>> I have been testing PETSc's scalability on clusters for matrices of sizes >>> 2000, 10,000, uptill 60,000. >>> >> >> 1) These matrices are incredibly small. We usually recommend 10,000 >> unknowns/process for weak scaling. You >> might get some benefit from a shared memory implementation on a >> multicore. >> >> >>> All I did was try to solve Ax=b for these matrices. I found that the >>> solution time dips if I use upto 16 or 32 processors. However for a larger >>> number of processors however the solution time seems to go up rather than >>> down. IS there anyway I can make my code strongly scalable ? >>> >> >> 2) These are small enough that direct factorization should be the fastest >> alternative. I would try UMFPack, SuperLU, and MUMPS. >> >> Matt >> >> >>> I am measuring the total time (sec) and KSP_SOLVE time in the >>> -log_summary output. Both times show the same behaviour described above. >>> >>> Gaurish >>> >> -- >> What most experimenters take for granted before they begin their >> experiments is infinitely more interesting than any results to which their >> experiments lead. >> -- Norbert Wiener >> > > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20110307/54c8204f/attachment-0001.htm>
