arXiv subjects

Whit Schonbein

Publications and source records attributed to Whit Schonbein.

4 recordsLinked to original sources

arXiv2026

RAMC: Remote Access Memory Channels over HPE Slingshot

In this paper, we present Remote Access Memory Channels (RAMC), an explicit one-sided communication library designed to leverage the capabilities of HPE Cray Slingshot network hardware. Existing one-sided communication frameworks, such as MPI RMA and OpenSHMEM, rely on monolithic shared memory models that introduce scalability and usability challenges. These frameworks often assume symmetric memory regions or require blocking collective operations for window creation, which can mismatch user communication needs and hinder performance. Implicit models, such as PGAS and UPC, aim to simplify programming by treating local and remote memory as a unified region but ultimately rely on explicit mechanisms to implement data movement. MPI's recently-introduced partitioned communication API offers a persistent point-to-point interface but sacrifices the dynamic flexibility of RDMA. RAMC is designed to address these limitations. Based on the core concept of a persistent uni-directional communication channel, RAMC leverages Slingshot's unique memory region counters to enable efficient completion notification. Experiments with a RAMC-based heat diffusion code demonstrate RAMC has no difficulty scaling to 19.6 thousand processes across 250 nodes, and microbenchmark studies across multiple libfabric versions show RAMC can outperform Cray's proprietary MPI implementation (e.g., increases in bandwidth ranging from approx. 100%-130% for 1B-4KiB messages under libfabric 1.15.2, and from approx. 30%-45% under libfabric 2.3.1) while identifying additional areas for improvement, such as small message latencies.

cs.NI↗

arXiv2026

Co-Design and Evaluation of a CPU-Free MPI GPU Communication Abstraction and Implementation

Removing the CPU from the communication fast path is essential to efficient GPU-based ML and HPC application performance. However, existing GPU communication APIs either continue to rely on the CPU for communication or rely on APIs that place significant synchronization burdens on programmers. In this paper we describe the design, implementation, and evaluation of an MPI-based GPU communication API enabling easy-to-use, high-performance, CPU-free communication. This API builds on previously proposed MPI extensions and leverages HPE Slingshot 11 network card capabilities. We demonstrate the utility and performance of the API by showing how the API naturally enables CPU-free gather/scatter halo exchange communication primitives in the Cabana/Kokkos performance portability framework, and through a performance comparison with Cray MPICH on the Frontier and Tuolumne supercomputers. Results from this evaluation show up to a 50% reduction in medium message latency in simple GPU ping-pong exchanges and a 28% speedup improvement when strong scaling a halo-exchange benchmark to 8,192 GPUs of the Frontier supercomputer.

cs.DC↗

arXiv2026

Scaling All-to-all Operations Across Emerging Many-Core Supercomputers

Performant all-to-all collective operations in MPI are critical to fast Fourier transforms, transposition, and machine learning applications. There are many existing implementations for all-to-all exchanges on emerging systems, with the achieved performance dependent on many factors, including message size, process count, architecture, and parallel system partition. This paper presents novel all-to-all algorithms for emerging many-core systems. Further, the paper presents a performance analysis against existing algorithms and system MPI, with novel algorithms achieving up to 3x speedup over system MPI at 32 nodes of state-of-the-art Sapphire Rapids systems.

cs.DC↗

arXiv2023

Measuring Thread Timing to Assess the Feasibility of Early-bird Message Delivery

Early-bird communication is a communication/computation overlap technique that combines fine-grained communication with partitioned communication to improve application run-time. Communication is divided among the compute threads such that each individual thread can initiate transmission of its portion of the data as soon as it is complete rather than waiting for all of the threads. However, the benefit of early-bird communication depends on the completion timing of the individual threads. In this paper, we measure and evaluate the potential overlap, the idle time each thread experiences between finishing their computation and the final thread finishing. These measurements help us understand whether a given application could benefit from early-bird communication. We present our technique for gathering this data and evaluate data collected from three proxy applications: MiniFE, MiniMD, and MiniQMC. To characterize the behavior of these workloads, we study the thread timings at both a macro level, i.e., across all threads across all runs of an application, and a micro level, i.e., within a single process of a single run. We observe that these applications exhibit significantly different behavior. While MiniFE and MiniQMC appear to be well-suited for early-bird communication because of their wider thread distribution and more frequent laggard threads, the behavior of MiniMD may limit its ability to leverage early-bird communication.

cs.DC↗