Hmm. There are modules of NWChem that have datasets capable of scaling from 1s to 100's of thousands of cores.
Right. Those don't need a fast interconnect. They probably also would run fine with MPI-1. That's a solved problem; we don't need to think much about it.
No, that's not true in the slightest for what Vinod is referring to. NWChem's CCSD(T) code hit 0.357 petaflops at 0.55% efficiency on Jaguar and this method is anything but simple. The most scalable portion is a 7-loop accumulation wherein the first loop computes very large intermediates (by design, it fills up the memory) which must be communicated all over the place in a non-trivial way along with other intermediates and permanent data inside of another set of do loops. Once all the buffers get pushed around, the inner loops are just a bunch of DGEMMs. See the attached papers for the details of the algorithm. The GA/ARMCI implementation is less than 1000 lines of code. Please let me know when you can match this with MPI-1.
I think this nicely illustrates my point that I don't know of any existing HPC application that really needs one-sided hardware to get great performance.*
Frankly, this is just a religious war already waged in HPCWire (Myricom versus IBM). It appears you're saying that IBM and Cray supporting powerful one-sided hardware is a waste of money. Is that why their machines, SGI's and those running Infiniband (excellent RDMA) compose the first 26 slots on the Top500 list? Anti-one-sided Myricom's best showing is #27. If you want to make a real argument against one-sided communication, show me an MPI-1-based CCSD(T) code that hits a third of a petaflop. Show me the code. Jeff -- Jeff Hammond The University of Chicago http://home.uchicago.edu/~jhammond/