ASCENT: Collaborative Research: Scaling Distributed AI Systems based on Universal Optical I/O

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Our society is rapidly becoming reliant on neural networks based artificial intelligence computation. New algorithms are invented daily, increasing the memory and computational requirements for both inference and training. This explosive growth has created an enormous demand for distributed machine learning (ML) training and inference. Estimates by OpenAI illustrate the steady growth of computational requirements of 100x every two years since 2012, which is a 50x faster than the rate of computation improvements enabled previously through Moore’s Law of semiconductor industry that we have enjoyed in the last half-century. This new computation demand has been partly met by rapid development of hardware accelerators and software stacks to support these specialized computations. Hardware accelerators have provided a significant amount of speed-up but today’s training tasks can still take days and even weeks. The reason for this: as the number of workers (e.g. compute nodes) increases, the computation time per worker decreases, but the communication requirements between the nodes increase, creating a bottleneck in the interconnect between the compute nodes. Future distributed ML systems will require 1-2 orders of magnitude higher interconnect bandwidth per node, creating a pressing need for entirely new ways to build interconnects for distributed ML systems. This proposal aims to create a new paradigm for scaling distributed ML computation, by developing a scalable interconnect solution based on advancing the integrated electronics and photonics technology that enables direct node-to-node optical fiber connectivity. The proposed cross-stack collaborative multi-disciplinary work will enable the education and training of a unique crop of engineers and scientists that cross the boundaries of machine learning, networking, and electronic-photonic systems and devices, which are in severe demand. The principal investigators have an established track record of direct engagement with high-school students providing summer internships at Berkeley Wireless Research Center and MIT’s Women’s Technology Program, as well as exemplary undergraduate research activities at Boston University. The educational and outreach activities the PIs have put in place will ensure early exposure and continued training of new generation of leaders in this field, from K-12, through undergraduate and graduate studies, and continuing workforce education, with special focus on underrepresented students.The interconnect has emerged as the key bottleneck in enabling the full potential of distributed ML. Future ML workloads are likely to require tens of Tbps of bandwidth per device. Ubiquitous deployment of logically-connected, physically distributed computation across shelf, rack and row scale can only be enabled by a new universal I/O that enables socket to socket communication at the energy, latency and bandwidth density of in-package interconnects. No such technology currently exists. Silicon-photonics based optical I/O has the potential to address this critical challenge, but fundamental advances–from chip manufacturing to routing algorithms–are still needed to ensure the scalability of these interconnect systems. To enable high-bandwidth density and energy-efficiency, dense wavelength division multiplexing must be used. High-efficiency ring resonator-based modulators and comb laser sources are needed to enable Tbps rates over each fiber connection and socket bandwidth scaling from 10s to 100s of Tbps. New link architectures like the proposed laser-forwarded coherent link are needed to enable high-efficiency external centralized comb laser sources with modest (sub-mW) power per wavelength per fiber port. The proposed work will also develop new scheduling algorithms, network architectures, and workload parallelism strategy to leverage the bandwidth density and low-latency of the universal optical I/O, to map large AI workloads with massive datasets to a scalable distributed compute system.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.