Hi, I am not familiar with you project. Tell us more. In order to achieve lowest latency (or overhead, depending on your optimization, or a blend thereof), a protocol designer might not want to pay for fixed costs that once amortized over long transfers yields more long transfer performance. Classic Fixed vs variable cost situation. The classic trades in two-sided are zero copy for long and two copy for short. If you have evidence to the contrary, great... Lots of people reported in the past the effect of a tradeoff as I described coming from the complex semantics of the mpi one sided api. One also has to ask if we can get even lower latency with less complex protocol too imho. Do you get both lower latency than two sided short msgs and higher bandwidth than two sided? What is the baseline of performance for two sided? Is it optimized? :-) Tony Anthony Skjellum, PhD Verari Systems, Inc +1-205-807-4968 -----Original Message----- From: Jeff Hammond <[email protected]> Date: Thu, 23 Apr 2009 20:03:07 To: Main MPI Forum mailing list<[email protected]> Subject: Re: [Mpi-forum] MPI-3 One-Sided Communications What does "allow for potentially lower bandwidth on long transfers as a side effect" mean? That one-sided should have lower latency at the expense of lower bandwidth? That's an unnecessary and intolerable compromise. ARMCI proves that one-sided bandwidth can equal if not beat MPI (http://www.emsl.pnl.gov/docs/parsoft/armci/performance.htm). Jeff On Thu, Apr 23, 2009 at 7:32 PM, Anthony Skjellum <[email protected]> wrote:

Hi, I was giving my opinion...

The main requirements for one sided was achieve lower latency than two sided (as well as one sidedness), and allow for potentially lower bandwidth on long transfers as a side effect... What one sided achieved is higher latency and higher bandwidth in typical (quality) implementations. �The api is consequently a mismatch to its original purpose... It diverged from its design center.. Missed the mark... Way too complex compared to simple put and get.

Starting again from first principles with the goal of very low latency remote put and get without the legacy of existing one sided is my suggestion.

In other words : Start over.

Perhaps that is why now we have an active messages group? Not sure.

Tony Anthony Skjellum, PhD Professor and Chair Dept. of Computer and Information Sciences University of Alabama at Birmingham +1-205-807-4968

-----Original Message----- From: Vinod tipparaju <[email protected]>

Date: Thu, 23 Apr 2009 20:09:38 To: <[email protected]> Subject: Re: [Mpi-forum] MPI-3 One-Sided Communications

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