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Opening Remarks Tue 6 Apr 08:00 a.m.  

Alex Dimakis · Ion Stoica · Alexander Smola

After the opening remarks, please join William Dally's invited talk, Directions for Deep Learning Hardware.


Invited Talk: William Dally

Directions for Deep Learning Hardware

Deep learning has been enabled by powerful hardware and its progress is gated by improvements in hardware performance. This talk will review the current state of deep learning hardware and explore a number of directions to continue performance scaling in the absence of Moore’s Law.. Topics discussed will include number representation, sparsity, memory organization, optimized circuits, and analog computation.

Bill is Chief Scientist and Senior Vice President of Research at NVIDIA Corporation and an Adjunct Professor and former chair of Computer Science at Stanford University. Bill is currently working on developing hardware and software to accelerate demanding applications including machine learning, bioinformatics, and logical inference. He has a history of designing innovative and efficient experimental computing systems. While at Bell Labs Bill contributed to the BELLMAC32 microprocessor and designed the MARS hardware accelerator. At Caltech he designed the MOSSIM Simulation Engine and the Torus Routing Chip which pioneered wormhole routing and virtual-channel flow control. At the Massachusetts Institute of Technology his group built the J-Machine and the M-Machine, experimental parallel computer systems that pioneered the separation of mechanisms from programming models and demonstrated very low overhead synchronization and communication mechanisms. At Stanford University his group developed the Imagine processor, which introduced the concepts of stream processing and partitioned register organizations, the Merrimac supercomputer, which led to GPU computing, and the ELM low-power processor. Bill is a Member of the National Academy of Engineering, a Fellow of the IEEE, a Fellow of the ACM, and a Fellow of the American Academy of Arts and Sciences. He has received the ACM Eckert-Mauchly Award, the IEEE Seymour Cray Award, the ACM Maurice Wilkes award, the IEEE-CS Charles Babbage Award, the IPSJ FUNAI Achievement Award, the Caltech Distinguished Alumni Award, and the Stanford Tau-Beta-Pi Teaching Award. He currently leads projects on computer architecture, network architecture, circuit design, and programming systems. He has published over 250 papers in these areas, holds over 160 issued patents, and is an author of the textbooks, Digital Design: A Systems Approach, Digital Systems Engineering, and Principles and Practices of Interconnection Networks.



Oral: Session 1: Search and Devices Tue 6 Apr 09:30 a.m.  

ModularNAS: Towards Modularized and Reusable Neural Architecture Search
Yunfeng Lin, Guilin Li, Xing Zhang, Weinan Zhang, Bo Chen, Ruiming Tang, Zhenguo Li, Jiashi Feng, Yong Yu

Automated neural architecture search (NAS) methods have been demonstrated as a powerful tool to facilitate neural architecture design. However, the broad applicability of NAS has been restrained due to the difficulty of designing task-specific search spaces and the necessity and verbosity to implement every NAS component from scratch when switching to another search space. In this work, we propose ModularNAS, a framework that implements essential components of NAS in a modularized and unified manner. It enables automatic search space generation for customized use cases while reusing predefined search strategies, with little extra work needed for each case. We conduct extensive experiments to verify the improved model performance on various tasks by reusing supported NAS components over customized search spaces. We have also shown that targeting existing architectures, ModularNAS can find superior ones concerning accuracy and deployment efficiency, such as latency and FLOPS. The source code of our framework can be found at https://github.com/huawei-noah/vega/tree/master/vega/algorithms/nas/modnas.

Fluid: Resource-aware Hyperparameter Tuning Engine
Peifeng Yu, Amber Liu, Mosharaf Chowdhury

Current hyperparameter tuning solutions lack complementary execution engines to efficiently leverage distributed computation, thus ignoring the possibility of intra- and inter-GPU sharing, which exhibits poor resource usage. In this paper, we present Fluid, a generalized hyperparameter tuning execution engine, that coordinates between hyperparameter tuning jobs and cluster resources. Fluid schedules evaluation trials in such jobs using a water-filling approach to make the best use of resources both at intra- and inter-GPU granularities to speed up the tuning process. By abstracting a hyperparameter tuning job as a sequence of TrialGroup, Fluid can boost the performance of diverse hyperparameter tuning solutions. Our experiments show that Fluid can speed up synchronous BOHB by 200%, and BOHB and ASHA by 30% while having similar final accuracy.

MicroNets: Neural Network Architectures for Deploying TinyML Applications on Commodity Microcontrollers
Colby Banbury, Chuteng Zhou, Igor Fedorov, Ramon Matas, Urmish Thakker, Dibakar Gope, Vijay Janapa Reddi, Matthew Mattina, Paul Whatmough

Executing machine learning workloads locally on resource constrained microcontrollers (MCUs) promises to drastically expand the application space of IoT. However, so-called TinyML presents severe technical challenges, as deep neural network inference demands a large compute and memory budget. To address this challenge, neural architecture search (NAS) promises to help design accurate ML models that meet the tight MCU memory, latency, and energy constraints. A key component of NAS algorithms is their latency/energy model, i.e., the mapping from a given neural network architecture to its inference latency/energy on an MCU. In this paper, we observe an intriguing property of NAS search spaces for MCU model design: on average, model latency varies linearly with model operation (op) count under a uniform prior over models in the search space. Exploiting this insight, we employ differentiable NAS (DNAS) to search for models with low memory usage and low op count, where op count is treated as a viable proxy to latency. Experimental results validate our methodology, yielding our MicroNet models, which we deploy on MCUs using Tensorflow Lite Micro, a standard open-source neural network (NN) inference runtime widely used in the TinyML community. MicroNets demonstrate state-of-the-art results for all three TinyMLperf industry-standard benchmark tasks: …

Characterizing and Taming Model Instability Across Edge Devices
Eyal Cidon, Jenya Pergament, Zain Asgar, Asaf Cidon, Sachin Katti

The same machine learning model running on different edge devices may produce highly-divergent outputs on a nearly-identical input. Possible reasons for the divergence include differences in the device sensors, the device's signal processing hardware and software, and its operating system and processors. This paper presents the first methodical characterization of the variations in model prediction across real-world mobile devices. We demonstrate that accuracy is not a useful metric to characterize prediction divergence, and introduce a new metric, instability, which captures this variation. We characterize different sources for instability, and show that differences in compression formats and image signal processing account for significant instability in object classification models. Notably, in our experiments, 14-17% of images produced divergent classifications across one or more phone models. We evaluate three different techniques for reducing instability. In particular, we adapt prior work on making models robust to noise in order to fine-tune models to be robust to variations across edge devices. We demonstrate our fine-tuning techniques reduce instability by 75%.


Oral: Session 2: Compilers Tue 6 Apr 11:10 a.m.  

Cortex: A Compiler for Recursive Deep Learning Models
Pratik Fegade, Tianqi Chen, Phillip Gibbons, Todd Mowry

Optimizing deep learning models is generally performed in two steps: (i) high-level graph optimizations such as kernel fusion and (ii) low level kernel optimizations such as those found in vendor libraries. This approach often leaves significant performance on the table, especially for the case of recursive deep learning models. In this paper, we present Cortex, a compiler-based approach to generate highly-efficient code for recursive models for low latency inference. Our compiler approach and low reliance on vendor libraries enables us to perform end-to-end optimizations, leading to up to 14X lower inference latencies over past work, across different backends.

A Deep Learning Based Cost Model for Automatic Code Optimization
Riyadh Baghdadi, Massinissa Merouani, Mohamed-Hicham LEGHETTAS, Kamel Abdous, Taha Arbaoui, Karima BENATCHBA, Saman Amarasinghe

Enabling compilers to automatically optimize code has been a longstanding goal for the compiler community. Efficiently solving this problem requires using precise cost models. These models predict whether applying a sequence of code transformations reduces the execution time of the program. Building an analytical cost model to do so is hard in modern x86 architectures due to the complexity of the microarchitecture. In this paper, we present a novel deep learning based cost model for automatic code optimization. This model was integrated in a search method and implemented in the Tiramisu compiler to select the best code transformations. The input of the proposed model is a set of simple features representing the unoptimized code and a sequence of code transformations. The model predicts the speedup expected when the code transformations are applied. Unlike previous models, the proposed one works on full programs and does not rely on any heavy feature engineering. The proposed model has only 16% of mean absolute percentage error in predicting speedups on full programs. The proposed model enables Tiramisu to automatically find code transformations that match or are better than state-of-the-art compilers without requiring the same level of heavy feature engineering required by those compilers

Learning Fitness Functions for Machine Programming
Shantanu Mandal, Todd Anderson, Javier Turek, Justin Gottschlich, Shengtian Zhou, Abdullah Muzahid

The problem of automatic software generation has been referred to as machine programming. In this work, we propose a framework based on genetic algorithms to help make progress in this domain. Although genetic algorithms (GAs) have been successfully used for many problems, one criticism is that hand-crafting GAs fitness function, the test that aims to effectively guide its evolution, can be notably challenging. Our framework presents a novel approach to learn the fitness function using neural networks to predict values of ideal fitness functions.We also augment the evolutionary process with a minimally intrusive search heuristic. This heuristic improves the framework’s ability to discover correct programs from ones that are approximately correct and does so with negligible computational overhead. We compare our approach with several state-of-the-art program synthesis methods and demonstrate that it finds more correct programs with fewer candidate program generations.

CODE: Compiler-based Neuron-aware Ensemble training
Ettore M. G. Trainiti, Thanapon Noraset, David Demeter, Doug Downey, Simone Campanoni Campanoni

Deep Neural Networks (DNNs) are redefining the state-of-the-art performance in a variety of tasks like speech recognition and image classification. These impressive results are often enabled by ensembling many DNNs together. Surprisingly, ensembling is often done by training several DNN instances from scratch and combining them. This paper shows that there is significant redundancy in today's way of ensembling. The novelty we propose is CODE, a compiler approach designed to automatically generate DNN ensembles while avoiding unnecessary retraining among its DNNs. For this purpose, CODE introduces neuron-level analyses and transformations aimed at identifying and removing redundant computation from the networks that compose the ensemble. Removing redundancy enables CODE to train large DNN ensembles in a fraction of the time and memory footprint needed by current techniques. These savings can be leveraged by CODE to increase the output quality of its ensembles.


Oral: Session 3: Communication and Storage Tue 6 Apr 01:30 p.m.  

Pufferfish: Communication-efficient Models At No Extra Cost
Hongyi Wang, Saurabh Agarwal, Dimitrios Papailiopoulos

To mitigate communication overheads in distributed model training, several studies propose the use of compressed stochastic gradients, usually achieved by sparsification or quantization. Such techniques achieve high compression ratios, but in many cases incur either significant computational overheads or some accuracy loss. In this work, we present Pufferfish, a communication and computation efficient distributed training framework that incorporates the gradient compression into the model training process via training low-rank, pre-factorized deep networks. Pufferfish not only reduces communication, but also completely bypasses any computation overheads related to compression, and achieves the same accuracy as state-of-the-art, off-the-shelf deep models. Pufferfish can be directly integrated into current deep learning frameworks with minimum implementation modification. Our extensive experiments over real distributed setups, across a variety of large-scale machine learning tasks, indicate that Pufferfish achieves up to 1.64x end-to-end speedup over the latest distributed training API in PyTorch without accuracy loss. Compared to the Lottery Ticket Hypothesis models, Pufferfish leads to equally accurate, small-parameter models while avoiding the burden of ``winning the lottery''. Pufferfish also leads to more accurate and smaller models than SOTA structured model pruning methods.

In-network Aggregation for Shared Machine Learning Clusters
Nadeen Gebara, Manya Ghobadi, Costa Paolo

We present PANAMA, a network architecture for machine learning (ML) workloads on shared clusters where a variety of training jobs co-exist.PANAMA consists of two key components: (i) an efficient in-network hardware accelerator designed to accelerate large data-parallel training transfers; and (ii) a lightweight congestion control protocol to enable fair sharing of network resources across different flows. Our congestion control protocol exploits the unique communication pattern in training to ensure large in-network aggregation transfers do not negatively impact short latency-sensitive flows. To evaluate the feasibility of PANAMA, we build an FPGA-based prototype with 10 Gbps transceivers and show that our hardware datapath achieves line-rate aggregation. Our large-scale simulations demonstrate that PANAMA improves the mean and 99%-tile completion time of latency-sensitive short flows by a factor of 2–4.5 while reducing the average training time of large jobs by a factor of 1.25.

Data Movement Is All You Need: A Case Study on Optimizing Transformers
Andrei Ivanov, Nikoli Dryden, Tal Ben-Nun, Shigang Li, Torsten Hoefler

Transformers are one of the most important machine learning workloads today. Training one is a very compute-intensive task, often taking days or weeks, and significant attention has been given to optimizing transformers. Despite this, existing implementations do not efficiently utilize GPUs. We find that data movement is the key bottleneck when training. Due to Amdahl's Law and massive improvements in compute performance, training has now become memory-bound. Further, existing frameworks use suboptimal data layouts. Using these insights, we present a recipe for globally optimizing data movement in transformers. We reduce data movement by up to 22.91% and overall achieve a 1.30x performance improvement over state-of-the-art frameworks when training a BERT encoder layer and 1.19x for the entire BERT. Our approach is applicable more broadly to optimizing deep neural networks, and offers insight into how to tackle emerging performance bottlenecks.

Learning on Distributed Traces for Data Center Storage Systems
Giulio Zhou, Martin Maas

Storage services in data centers continuously make decisions, such as for cache admission, prefetching, and block allocation. These decisions are typically driven by heuristics based on statistical properties like temporal locality or common file sizes. The quality of decisions can be improved through application-level information such as the database operation a request belongs to. While such features can be exploited through application hints (e.g., explicit prefetches), this process requires manual work and is thus only viable for the most tuned workloads.

In this work, we show how to leverage application-level information automatically, by building on distributed traces that are already available in warehouse-scale computers. As these traces are used for diagnostics and accounting, they contain information about requests, including those to storage services. However, this information is mostly unstructured (e.g., arbitrary text) and thus difficult to use. We demonstrate how to do so automatically using machine learning, by applying ideas from natural language processing.

We show that different storage-related decisions can be learned from distributed traces, using models ranging from simple clustering techniques to neural networks. Instead of designing specific models for different storage-related tasks, we show that the same models can be used as building blocks for different tasks. …


Oral: Session 4: Training (I) Tue 6 Apr 03:20 p.m.  

TensorFlow Lite Micro: Embedded Machine Learning for TinyML Systems
Robert David, Jared Duke, Advait Jain, Vijay Janapa Reddi, Nat Jeffries, Jian Li, Nick Kreeger, Ian Nappier, Meghna Natraj, Tiezhen Wang, Pete Warden, Rocky Rhodes, Rocky Rhodes

We introduce TensorFlow (TF) Micro, an open-source machine learning inference framework for running deep-learning models on embedded systems. TF Micro tackles the efficiency requirements imposed by embedded system resource constraints and the fragmentation challenges that make cross-platform interoperability nearly impossible. The framework adopts a unique interpreter-based approach that provides flexibility while overcoming the challenges. This paper explains the design decisions behind TF Micro and describes its implementation. We present an evaluation to demonstrate its low resource requirement and minimal run-time performance overhead.

Scaling Distributed Training with Adaptive Summation
Saeed Maleki, Madan Musuvathi, Todd Mytkowicz, Olli Saarikivi, Tianju Xu, Vadim Eksarevskiy, Jaliya Ekanayake, Emad Barsoum

Data parallelism is a common way to parallelize stochastic gradient descent (SGD). However, the loss of convergence at large minibatch sizes limits the scalability of data parallelism. This paper introduces a novel method to combine gradients called Adasum that significantly improves the convergence when using large minibatches. This paper provides the intuition and formal justification of Adasum along with a convergence proof. Additionally, the paper describes an efficient implementation of Adasum and its integration into the open-source toolkit Horovod for use in both TensorFlow and PyTorch.

The paper empirically shows that Adasum improves convergence when using large minibatch sizes for multiple optimizers (Momentum-SGD, Adam, and LAMB). For BERT-Large training with a minibatch size of 64K, using both Adasum and LAMB training converges in 20% fewer epochs than with LAMB alone. This combination also allows BERT-Large training to scale to a 128K minibatch size. While one of the motivations for LAMB was the inability of the Adam optimizer to scale beyond a minibatch size of 16K, we show that Adasum helps Adam scale BERT-Large training to a 64K minibatch size. Our implementation of Adasum in Horovod has already been adopted in several production environments.

PipeMare: Asynchronous Pipeline Parallel DNN Training
Bowen Yang, Jian Zhang, Jonathan Li, Christopher Re, Christopher Aberger, Christopher De Sa

Pipeline parallelism when training neural networks enables models to be partitioned spatially, which can lead to overall higher hardware utilization. Unfortunately, to preserve the statistical efficiency of sequential training, existing pipeline parallel training techniques sacrifice hardware efficiency by decreasing pipeline utilization or incurring extra memory costs. In this paper, we investigate to what extent these sacrifices will be necessary on the emerging class of new dataflow hardware accelerators. We devise PipeMare, a simple yet robust training method that tolerates asynchronous updates during pipeline parallel execution without sacrificing utilization or memory, which allows efficient use of fine-grained pipeline parallelism. Concretely, when tested on ResNet and Transformer networks, asynchrony enables PipeMare to use up to 2.7x less memory or get 14.3x higher pipeline utilization, with similar model quality, when compared to state-of-the-art synchronous pipeline parallel training techniques.

EXPLORING THE LIMITS OF CONCURRENCY IN ML TRAINING ON GOOGLE TPUS
Sameer Kumar, Yu (Emma) Wang, Cliff Young, James Bradbury, Naveen Kumar, Dehao Chen, Andy Swing

Recent results in language understanding using neural networks have required training hardware of unprecedented scale, with thousands of chips cooperating on a single training run. This paper presents techniques to scale ML models on the Google TPU Multipod, a mesh with 4096 TPU-v3 chips. We discuss model parallelism to overcome scaling limitations from the fixed batch size in data parallelism, communication/collective optimizations, distributed evaluation of training metrics, and host input processing scaling optimizations. These techniques are demonstrated in both the TensorFlow and JAX programming frameworks. We also present performance results from the recent Google submission to the MLPerf-v0.7 benchmark contest, achieving record training times from 16 to 28 seconds in four MLPerf models on the Google TPU-v3 Multipod machine.

TT-Rec: Tensor Train Compression for Deep Learning Recommendation Models
Chunxing Yin, Bilge Acun, Carole-Jean Wu, Xing Liu

The memory capacity of embedding tables in deep learning recommendation models (DLRMs) is increasing dramatically from tens of GBs to TBs across the industry. Given the fast growth in DLRMs, novel solutions are urgently needed in order to enable DLRM innovations. At the same time, this must be done in a fast and efficient way without having to exponentially increase infrastructure capacity demands. In this paper, we demonstrate the promising potential of Tensor Train decomposition for DLRMs (TT-Rec), an important yet under-investigated context. We design and implement optimized kernels (TT-EmbeddingBag) to evaluate the proposed TT-Rec design. TT-EmbeddingBag is 3x faster than the SOTA TT implementation. The performance of TT-Rec is further optimized with the batched matrix multiplication and caching strategies for embedding vector lookup operations. In addition, we present mathematically and empirically the effect of weight initialization distribution on DLRM accuracy and propose to initialize the tensor cores of TT-Rec following the sampled Gaussian distribution. We evaluate TT-Rec across three important design space dimensions---memory capacity, accuracy, and timing performance---by training MLPerf-DLRM with Criteo's Kaggle and Terabyte data sets. TT-Rec compresses the model size by 4x to 221x for Kaggle, with 0.03% to 0.3% loss of accuracy correspondingly. For Terabyte, our …