Background and Related Work

Our work describes and analyzes the implementation of the OpenSHMEM specification using a modern fabric interface. In this section, we provide an overview of these topics and some of the most closely related works.

Fabric Interfaces

A variety of low-level communication APIs have been used in HPC for high performance networking, including the OpenFabrics Alliance (OFA) Verbs API,

PAMI [19], Portals [2], and uGNI [8]. Often, such low-level APIs are customized to leverage specific system architectures. Recently, the industry has trended toward exchanging system-specific APIs for open, portable fabric interfaces that provide a low-level interface to fabric services while minimizing ties to specific architectures. This approach promises to provide better portability for communication middleware, such as OpenSHMEM, while maximizing the exposure of application-level communication semantics to the fabric to enable aggressive optimization.

OpenFabrics Interfaces

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The OpenFabrics Alliance (OFA) provides open- source software for high-performance networking applications that demand low latency and high bandwidth. Historically, the only fabric interface offered by the OFA was the Verbs API as defined in the InfiniBand* specification. As the InfiniBand specification was originally envisioned as a generic system I/O interconnect, there are semantic differences between Verbs and the requirements of PGAS libraries and languages. These semantic mismatches require unnecessary adaptations in PGAS implementations, such as OpenSHMEM, resulting in significant software overhead [21].

The OFA has created a working group, called the OpenFabrics Interfaces Working Group (OFIWG), that aims to define a fabric interface that has a tight semantic map to various applications classes that use it, including PGAS programming models. Members of the PGAS community provided input into the design of the new fabric interfaces to help improve the mapping of PGAS features onto fabric interface features. The fabric library created from this effort is called libfabric. It consists of two logically distinct components: A set of fabric providers that implement the communication interfaces for a particular fabric hardware, and a general purpose framework that provides a plugin-like capability for providers. In the rest of the paper, we use the term uGNI provider to imply the specific implementation of libfabric interfaces for the Aries interconnect. Lib- fabric is freely available from Github [20], and is distributed via the OpenFabrics Enterprise Distribution (OFED) as well as popular Linux distributions.

 
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