On Tue, Jun 16, 2009 at 1:13 PM, Alex Peyser <peyser.alex at gmail.com> wrote:
> On Tuesday 16 June 2009 01:53:35 pm Matthew Knepley wrote: > > On Tue, Jun 16, 2009 at 12:38 PM, xiaoyin ji > > <sapphire.jxy at gmail.com<mailto:sapphire.jxy at gmail.com>> wrote: Hi > > there, > > > > I'm using PETSc MATMPIAIJ and ksp solver. It seems that PETSc will run > > obviously faster if I set the number of CPUs close to the number of > > computer nodes in the job file. By default MPIAIJ matrix is stored in > > different processors and ksp solver will communicate for each step, > > however since on each node several CPUs share the same memory while > > ksp may still try to communicate through network card, this may mess > > up a bit. Is there any way to detect which CPUs are sharing the same > > memory? Thanks a lot. > > > > The interface for this is mpirun or the job submission mechanism. > > > > Matt > > > > > > Best, > > Xiaoyin Ji > > -- > > 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 > > I had a question on what is the best approach for this. Most of the time is > spent inside of BLAS, correct? So wouldn't you maximize your operations by > running one MPI/PETSC job per board (per shared memory), and use a > multi-threaded BLAS that matches your board? You should cut down > communications by some factor proportional to the number of threads per > board, and the BLAS itself should better optimize most of your operations > across the board, rather than relying on higher order parallelisms. This is a common misconception. In fact, most time is spent in MatVec or BLAS1, neither of which benefit from MT BLAS. Matt > > Regards, > Alex Peyser > -- 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/20090616/c1c27497/attachment.htm>
