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  1. Free, publicly-accessible full text available July 30, 2024
  2. Manycore GPU architectures have become the mainstay for accelerating graph computations. One of the primary bottlenecks to performance of graph computations on manycore architectures is the data movement. Since most of the accesses in graph processing are due to vertex neighborhood lookups, locality in graph data structures plays a key role in dictating the degree of data movement. Vertex reordering is a widely used technique to improve data locality within graph data structures. However, these reordering schemes alone are not sufficient as they need to be complemented with efficient task allocation on manycore GPU architectures to reduce latency due to local cache misses. Consequently, in this article, we introduce a software/hardware co-design framework for accelerating graph computations. Our approach couples an architecture-aware vertex reordering with a priority-based task allocation technique. As the task allocation aims to reduce on-chip latency and associated energy, the choice of Network-on-Chip (NoC) as the communication backbone in the manycore platform is an important parameter. By leveraging emerging three-dimensional (3D) integration technology, we propose design of a small-world NoC (SWNoC)-enabled manycore GPU architecture, where the placement of the links connecting the streaming multiprocessors (SMs) and the memory controllers (MCs) follow a power-law distribution. The proposed 3D SWNoC-enabled software/hardware co-design framework achieves 11.1% to 22.9% performance improvement and 16.4% to 32.6% less energy consumption depending on the dataset and the graph application, when compared to the default order of dataset running on a conventional planar mesh architecture. 
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  3. Influence maximization aims to select k most-influential vertices or seeds in a network, where influence is defined by a given diffusion process. Although computing optimal seed set is NP-Hard, efficient approximation algorithms exist. However, even state-of-the-art parallel implementations are limited by a sampling step that incurs large memory footprints. This in turn limits the problem size reach and approximation quality. In this work, we study the memory footprint of the sampling process collecting reverse reachability information in the IMM (Influence Maximization via Martingales) algorithm over large real-world social networks. We present a memory-efficient optimization approach (called HBMax) based on Ripples, a state-of-the-art multi-threaded parallel influence maximization solution. Our approach, HBMax, uses a portion of the reverse reachable (RR) sets collected by the algorithm to learn the characteristics of the graph. Then, it compresses the intermediate reverse reachability information with Huffman coding or bitmap coding, and queries on the partially decoded data, or directly on the compressed data to preserve the memory savings obtained through compression. Considering a NUMA architecture, we scale up our solution on 64 CPU cores and reduce the memory footprint by up to 82.1% with average 6.3% speedup (encoding overhead is offset by performance gain from memory reduction) without loss of accuracy. For the largest tested graph Twitter7 (with 1.4 billion edges), HBMax achieves 5.9× compression ratio and 2.2× speedup. 
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  4. Graph application workloads are dominated by random memory accesses with poor locality. To tackle the irregular and sparse nature of computation, ReRAM-based Processing-in-Memory (PIM) architectures have been proposed recently. Most of these ReRAM architecture designs have focused on mapping graph computations into a set of multiply-and-accumulate (MAC) operations. ReRAMs also offer a key advantage in reducing memory latency between cores and memory by allowing for processing-in-memory (PIM). However, when implemented on a ReRAM-based manycore architecture, graph applications still pose two key challenges – significant storage requirements (particularly due to wasted zero cell storage), and significant amount of on-chip traffic. To tackle these two challenges, in this paper we propose the design of a 3D NoC-enabled ReRAM-based manycore architecture. Our proposed architecture incorporates a novel crossbar-aware node reordering to reduce ReRAM storage requirements. Secondly, its 3D NoC-enabled design reduces on-chip communication latency. Our architecture outperforms the state-of-the-art in ReRAM-based graph acceleration by up to 5x in performance while consuming up to 10.3x less energy for a range of graph inputs and workloads. 
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  5. We study the problem of designing scalable algorithms to find effective intervention strategies for controlling stochastic epidemic processes on networks. This is a common problem arising in agent based models for epidemic spread.Previous approaches to this problem focus on either heuristics with no guarantees or approximation algorithms that scale only to networks corresponding to county-sized populations, typically, with less than a million nodes. In particular, the mathematical-programming based approaches need to solve the Linear Program (LP) relaxation of the problem using an LP solver, which restricts the scalability of this approach. In this work, we overcome this restriction by designing an algorithm that adapts the multiplicative weights update (MWU) framework, along with the sample average approximation (SAA) technique, to approximately solve the linear program (LP) relaxation for the problem. To scale this approach further, we provide a memory-efficient algorithm that enables scaling to large networks, corresponding to country-size populations, with over 300 million nodes and 30 billion edges. Furthermore, we show that this approach provides near-optimal solutions to the LP in practice.

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