On Mon, Oct 13, 2008 at 10:08 AM, Christoph Statz <christoph.statz at ifn.et.tu-dresden.de> wrote: > Hello Matt and PETSc-users, > > 1) With any performance question, please send the output of -log_summary > > You'll find the output attached > (But there is _really_ not much to see).
I will look at it. > 2) I think it is unlikely that cache misses are responsible for this > performance. It is > much more likely that bandwidth limitations are responsible. > > As far as I can see, there are neither bandwidth limitations nor latency > problems (since there is an infiniband-interconnect). > MPI-Performance (Vampirtrace + Scalasca) looks good (late senders/receivers, > barriers etcpp.). > PAPI-Instrumentation says: cache misses. That stuff is rarely worth running. Without a decent model of the performance, the data is no help. I am not talking about network bandwidth, but memory bandwidth. For a sparse matvec that comes from a simple scalar PDE, you need incredible amounts of bandwidth to drive the tiny amount of flops. The equation is in the paper. > Please see the paper > by Kaushik and Gropp which models sparse matvec performance (on > Dinesh's website). > > Which Paper on which website. Please send a link. I believe you want 11 and 17 here http://www.mcs.anl.gov/~kaushik/ under the Publications link. > 3) You would see better performance using a block method. Sparse matvec > without > blocks will never see good percentages of peak (ditto for backsolve). > > How do I use the block methods? > Since I rely on the "user-level" interfaces kspsolve etcpp., I don't see how > i could influence this. You can't unless your system has block structure. If it does, you can use the BAIJ matrix types. Matt > You'll find basic source code attached. > Sincerly, > Christoph > -- > Christoph Statz > Institut f?r Nachrichtentechnik > Technische Universit?t Dresden > 01062 Dresden > Email: christoph.statz at mailbox.tu-dresden.de > Phone: +49 351 463 32287 > > > > > > -- 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
