On Tue, Sep 22, 2009 at 08:59:19AM +0200, [email protected] wrote: > > On Mon, Sep 21, 2009 at 09:44:11PM +0200, Johan Hake wrote: > >> On Monday 21 September 2009 21:37:03 Anders Logg wrote: > >> > Johan and I have set up a benchmark for parallel speedup in > >> > > >> > bench/fem/speedup > >> > > >> > Here are some preliminary results: > >> > > >> > Speedup | Assemble Assemble + solve > >> > -------------------------------------- > >> > 1 | 1 1 > >> > 2 | 1.4351 4.0785 > >> > 4 | 2.3763 6.9076 > >> > 8 | 3.7458 9.4648 > >> > 16 | 6.3143 19.369 > >> > 32 | 7.6207 33.699 > >> > > >> > These numbers look a bit strange, especially the superlinear speedup > >> > for assemble + solve. There might be a bug somewhere in the benchmark > >> > code. > >> > > >> > Anyway, we have some preliminary results that at least show some kind > >> > of speedup. > >> > > >> > It would be interesting to hear some comments on what kind of numbers > >> > we should expect to get from Matt and others. > >> > > >> > The benchmark is for assembling and solving Poisson on a 64 x 64 x 64 > >> > mesh using PETSc/MUMPS. Partitioning time is not included in the > >> > numbers. > >> > >> What solver is used when the number of processors is 1? If this is > >> different > >> from MUMPS, we will have the performance difference between the two > >> solvers > >> included in the speedup bump when going from 1 -> 2 processors. > > > > It's the default PETSc LU solver which should be UMFPACK. > > > > So one explanation could be that MUMPS is twice as fast as UMFPACK > > (looking at the speedup for two processes), which means we should > > divide the numbers by 2, giving a speedup of 17 instead of 34 which > > would be more reasonable. > > > > The total speedup of 17 includes both assemble + solve. Since assemble > > is obviously not scaling as it should, MUMPS may still be scaling > > pretty good. > > > > So some preliminary conclusions are: > > > > 1. Something is not right with assembly. > > > > 2. MUMPS scales well and runs relatively faster than UMFPACK. > > > > That MUMPS scales well probably also suggest that something is wrong with > the assembley. Is the solution of the problem correct ?
Haven't looked but it should be. The buildbots are running a system test for parallel assembly and comparing with the serial result and those tests pass. This example is simpler than that test. -- Anders
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