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.

Ahem. I think you just proved Greg's point. Jaguar is a Cray XT series. While I rather like that machine (I was part of the team at Sandia at the time), it has atrocious one-sided performance for small messages. If you can do it with big messages, you can do it with MPI-1 two sided.

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.

At this point, we are just bickering about where the work is, right? So, the app wants to program in a GA model for ease of use. Great. That isn't a performance argument.

...

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.

Um, yeah, Infiniband isn't up there because of its one-sided support. Neither is the Cray machine. Oh, wait, neither are the IBM machines. Keith