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1. TAP-2.5D: A Thermally-Aware Chiplet Placement Methodology for 2.5D Systems

   Ma, Yenai ; Delshadtehrani, Leila ; Demirkiran, Cansu ; Abellan, Jose L. ; Joshi, Ajay ( March 2021 , Design, Automation and Test in Europe (DATE))

   null (Ed.)

   Heterogeneous systems are commonly used today to sustain the historic benefits we have achieved through technology scaling. 2.5D integration technology provides a cost-effective solution for designing heterogeneous systems. The traditional physical design of a 2.5D heterogeneous system closely packs the chiplets to minimize wirelength, but this leads to a thermally-inefficient design. We propose TAP-2.5D: the first open-source network routing and thermally-aware chiplet placement methodology for heterogeneous 2.5D systems. TAP-2.5D strategically inserts spacing between chiplets to jointly minimize the temperature and total wirelength, and in turn, increases the thermal design power envelope of the overall system. We present three case studies demonstrating the usage and efficacy of TAP-2.5D. 

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2. Chiplet-Package Co-Design For 2.5D Systems Using Standard ASIC CAD Tools

   https://doi.org/10.1109/ASP-DAC47756.2020.9045734  

   Kabir, MD Arafat ; Peng, Yarui ( January 2020 , 2020 25th Asia and South Pacific Design Automation Conference (ASP-DAC))

   Chiplet integration using 2.5D packaging is gaining popularity nowadays which enables several interesting features like heterogeneous integration and drop-in design method. In the traditional die-by-die approach of designing a 2.5D system, each chiplet is designed independently without any knowledge of the package RDLs. In this paper, we propose a Chip-Package Co-Design flow for implementing 2.5D systems using existing commercial chip design tools. Our flow encompasses 2.5D-aware partitioning suitable for SoC design, Chip-Package Floorplanning, and post-design analysis and verification of the entire 2.5D system. We also designed our own package planners to route RDL layers on top of chiplet layers. We use an ARM Cortex-M0 SoC system to illustrate our flow and compare analysis results with a monolithic 2D implementation of the same system. We also compare two different 2.5D implementations of the same SoC system following the drop-in approach. Alongside the traditional die-by-die approach, our holistic flow enables design efficiency and flexibility with accurate cross-boundary parasitic extraction and design verification. 

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3. Fast thermal analysis for chiplet design based on graph convolution networks

   Chen, L. ; Jin, W. ; Tan, S. ( January 2022 , Proc. Asia South Pacific Design Automation Conference (ASP-DAC’22))

   2.5D chiplet-based technology promises an efficient integration technique for advanced designs with more functionality and higher performance. Temperature and related thermal optimization, heat removal are of critical importance for temperature-aware physical synthesis for chiplets. This paper presents a novel graph convolutional networks (GCN) architecture to estimate the thermal map of the 2.5D chiplet-based systems with the thermal resistance networks built by the compact thermal model (CTM). First, we take the total power of all chiplets as an input feature, which is a global feature. This additional global information can overcome the limitation that the GCN can only extract local information via neighborhood aggregation. Second, inspired by convolutional neural networks (CNN), we add skip connection into the GCN to pass the global feature directly across the hidden layers with the concatenation operation. Third, to consider the edge embedding feature, we propose an edge-based attention mechanism based on the graph attention networks (GAT). Last, with the multiple aggregators and scalers of principle neighborhood aggregation (PNA) networks, we can further improve the modeling capacity of the novel GCN. The experimental results show that the proposed GCN model can achieve an average RMSE of 0.31 K and deliver a 2.6$\times$ speedup over the fast steady-state solver of open-source {\it HotSpot} based on SuperLU. More importantly, the GCN model demonstrates more useful generalization or transferable capability. Our results show that the trained GCN can be directly applied to predict thermal maps of six unseen datasets with acceptable mean RMSEs of less than 0.67 K without retraining via inductive learning. 

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4. SPACX: Silicon Photonics-based Scalable Chiplet Accelerator for DNN Inference

   https://doi.org/10.1109/HPCA53966.2022.00066  

   Li, Yuan ; Louri, Ahmed ; Karanth, Avinash ( April 2022 , IEEE International Symposium on High-Performance Computer Architecture (HPCA))

   In pursuit of higher inference accuracy, deep neural network (DNN) models have significantly increased in complexity and size. To overcome the consequent computational challenges, scalable chiplet-based accelerators have been proposed. However, data communication using metallic-based interconnects in these chiplet-based DNN accelerators is becoming a primary obstacle to performance, energy efficiency, and scalability. The photonic interconnects can provide adequate data communication support due to some superior properties like low latency, high bandwidth and energy efficiency, and ease of broadcast communication. In this paper, we propose SPACX: a Silicon Photonics-based Chiplet ACcelerator for DNN inference applications. Specifically, SPACX includes a photonic network design that enables seamless single-chiplet and cross-chiplet broadcast communications, and a tailored dataflow that promotes data broadcast and maximizes parallelism. Furthermore, we explore the broadcast granularities of the photonic network and implications on system performance and energy efficiency. A flexible bandwidth allocation scheme is also proposed to dynamically adjust communication bandwidths for different types of data. Simulation results using several DNN models show that SPACX can achieve 78% and 75% reduction in execution time and energy, respectively, as compared to other state-of-the-art chiplet-based DNN accelerators. 

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5. CPElide: Efficient Multi-Chiplet GPU Implicit Synchronization

   Dalmia, Preyesh ; Shashi_Kumar, Rajesh ; Sinclair, Matthew D ( November 2024 , IEEE)

   Chiplets are transforming computer system designs, allowing system designers to combine heterogeneous computing resources at unprecedented scales. Breaking larger, monolithic chips into smaller, connected chiplets helps performance continue scaling, avoids die size limitations, improves yield, and reduces design and integration costs. However, chiplet-based designs introduce an additional level of hierarchy, which causes indirection and non-uniformity. This clashes with typical heterogeneous systems: unlike CPU-based multi-chiplet systems, heterogeneous systems do not have significant OS support or complex coherence protocols to mitigate the impact of this indirection. Thus, exploiting locality across application phases is harder in multi-chiplet heterogeneous systems. We propose CPElide, which utilizes information already available in heterogeneous systems’ embedded microprocessor (the command processor) to track inter-chiplet data dependencies and aggressively perform implicit synchronization only when necessary, instead of conservatively like the state-of-the-art HMG. Across 24 workloads CPElide improves average performance (13%, 19%), energy (14%, 11%), and network traffic (14%, 17%), respectively, over current approaches and HMG. 

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