In my prior blog entry, I answered the first of Durga C.’s questions to me.  Here’s all three of his questions:

1. What is the role of the hardware in an RDMA transaction?  In other words, why does one need special hardware (e.g., InfiniBand, iWARP, RoCE, etc.) hardware to do RDMA as opposed to a “normal” Ethernet NIC? (see prior blog entry)
2. Further, can you explain why pure software solutions (e.g., Open-MX) are better than nothing when you don’t have hardware support?
3. Also, what is the difference between “RDMA” and “RMA”?

Let’s explore the last two of those questions. Read More »

Tags: hardware, HPC, mpi, RDMA, RMA, software

Durga C., long-time listener, first-time caller, sent me a few interesting questions that I thought I’d share with everyone.  Here’s his first question:

1. What is the role of the hardware in an RDMA transaction?  In other words, why does one need special hardware (e.g., InfiniBand, iWARP, RoCE, etc.) hardware to do RDMA as opposed to a “normal” Ethernet NIC?

This one question is surprisingly complex.  Let’s dive in…

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Tags: hardware, HPC, mpi, RDMA, RMA, software

Today we feature a deep-dive guest post from Torsten Hoefler, the Performance Modeling and Simulation lead of the Blue Waters project at NCSA, and Pavan Balaji, computer scientist in the Mathematics and Computer Science (MCS) Division at the Argonne National Laboratory (ANL), and as a fellow of the Computation Institute at the University of Chicago.

Despite MPI’s vast success in bringing portable message passing to scientists on a wide variety of platforms, MPI has been labeled as a communication model that only supports “two-sided” and “global” communication. The MPI-1 standard, which was released in 1994, provided functionality for performing two-sided and group or collective communication. The MPI-2 standard, released in 1997, added support for one-sided communication or remote memory access (RMA) capabilities, among other things. However, users have been slow to adopt such capabilities because of a number of reasons, the primary ones being: (1) the model was too strict for several application behavior patterns, and (2) there were several missing features in the MPI-2 RMA standard. Bonachea and Duell put together a more-or-less comprehensive list of areas where MPI-2 RMA falls behind. A number of alternate programming models, including Global Arrays, UPC and CAF have gained popularity filling this gap.

That’s where MPI-3 comes in.

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Tags: HPC, mpi, MPI-3, RMA