On Tue, 16 Jun 2009, Alex Peyser wrote: > On Tuesday 16 June 2009 02:29:14 pm Matthew Knepley wrote: > > > > This is a common misconception. In fact, most time is spent in MatVec or > > BLAS1, neither of which benefit from MT BLAS.
> Interesting. At least my misconception is common. > That makes things tricky with ATLAS, since the number of threads is a > compile-time constant. I can't imagine it would be a good idea to have an 8x > BLAS running 8xs simultaneously -- unless the mpi jobs were all > unsynchronized. It may be only 10-20% of the time, but that's still a large > overlap of conflicting threads degrading performance. > > I'll have to do some benchmarks. Is the 10-20% number still true for fairly > dense matrices? Its just a number I pulled out of a hat [for sparse matrix solves]. -log_summary would be the correct thing for a given application. If using MATDENSE - a much higher percentage of time will be in blas. Satish > > Ah, another layer of administration-code may now be required to properly > allocate jobs. > > Alex >
