Title: EGIS: Entropy Guided Image Synthesis for Dataset-Agnostic Testing of RRAM-Based DNNs
While resistive random access memory (RRAM) based deep neural networks (DNN) are important for low-power inference in IoT and edge applications, they are vulnerable to the effects of manufacturing process variations that degrade their performance (classification accuracy). However, to test the same post-manufacture, the (image) dataset used to train the associated machine learning applications may not be available to the RRAM crossbar manufacturer for privacy reasons. As such, the performance of DNNs needs to be assessed with carefully crafted dataset-agnostic synthetic test images that expose anomalies in the crossbar manufacturing process to the maximum extent possible. In this work, we propose a dataset-agnostic post-manufacture testing framework for RRAM-based DNNs using Entropy Guided Image Synthesis (EGIS). We first create a synthetic image dataset such that the DNN outputs corresponding to the synthetic images minimize an entropy-based loss metric. Next, a small subset (consisting of 10-20 images) of the synthetic image dataset, called the compact image dataset, is created to expedite testing. The response of the device under test (DUT) to the compact image dataset is passed to a machine learning based outlier detector for pass/fail labeling of the DUT. It is seen that the test accuracy using such synthetic test images is very close to that of contemporary test methods.  more » « less
Award ID(s):
2414361
PAR ID:
10586788
Author(s) / Creator(s):
; ; ;
Publisher / Repository:
IEEE
Date Published:
Edition / Version:
1
Volume:
1
Issue:
1
Page Range / eLocation ID:
1-6
Subject(s) / Keyword(s):
DNN Testing, RRAM, Test images
Format(s):
Medium: X Size: 1 Other: 1
Size(s):
1
Location:
Lyon, France
Sponsoring Org:
National Science Foundation
More Like this
  1. Resistive Random-Access Memory (RRAM) crossbar array-based Deep Neural Networks (DNNs) are increasingly attractive for implementing ultra-low-power computing for AI. However, RRAM-based DNNs face inherent challenges from manufacturing process variability, which can compromise their performance (classification accuracy) and functional safety. One way to test these DNNs is to apply the exhaustive set of test images to each DNN to ascertain its performance; however, this is expensive and time-consuming. We propose a signature-based predictive testing (SiPT) in which a small subset of test images is applied to each DNN and the classification accuracy of the DNN is predicted directly from observations of the intermediate and final layer outputs of the network. This saves the test cost while allowing binning of RRAMbased DNNs for performance. To further improve the test efficiency of SiPT, we create the optimized compact set of test images, leveraging image filters and enhancements to synthesize images and develop a cascaded test structure, incorporating multiple sets of SiPT modules trained on compact test subsets of varying sizes. Through experimentation across diverse test cases, we demonstrate the viability of our SiPT framework under the RRAM process variations, showing test efficiency improvements. 
    more » « less
  2. Variability-induced accuracy degradation of RRAM based DNNs is of great concern due to their significant potential for use in future energy-efficient machine learning architectures. To address this, we propose a two-step process. First, an enhanced testing procedure is used to predict DNN accuracy from a set of compact test stimuli (images). This test response (signature) is simply the concatenated vectors of output neurons of intermediate final DNN layers over the compact test images applied. DNNs with a predicted accuracy below a threshold are then tuned based on this signature vector. Using a clustering based approach, the signature is mapped to the optimal tuning parameter values of the DNN (determined using off-line training of the DNN via backpropagation) in a single step, eliminating any post-manufacture training of the DNN weights (expensive). The tuning parameters themselves consist of the gains and offsets of the ReLU activation of neurons of the DNN on a per-layer basis and can be tuned digitally. Tuning is achieved in less than a second of tuning time, with yield improvements of over 45% with a modest accuracy reduction of 4% compared to digital DNNs. 
    more » « less
  3. Compute-in-memory (CiM) based convolutional neural network (CNN) accelerators achieve low-power inference, utilizing memristive crossbar arrays for matrix multiplications. However, inherent conductance variations within the crossbar introduce computational errors. These errors propagate to the CNN output and cause image misclassification, leading to sub stantial accuracy degradation. This paper addresses the critical challenge of efficient and reliable post-manufacture testing for CiM-based CNN accelerators. We propose a novel test image sampling methodology, which iteratively applies sampled im ages from the CNN’s testing dataset using progressive random sampling (PRS) to a device under test (DUT) and estimates a confidence interval for the DUT accuracy. Based on the confidence interval and the acceptable accuracy threshold, the test labels a DUT as ”pass” or ”fail”. Furthermore, if we have access to an initial set of DUTs, we apply the images from the CNN’s testing dataset to these DUTs and leverage the DUT outputs to rank-order test images. We develop a sequential estimation test (SET) framework, where the images from the CNN’s testing dataset are sequentially applied according to a predetermined rank and the test terminates when a DUT can be confidently labeled as “pass” or “fail” based on the applied images. In each case, the number of applied test images adapts to the quality of the DUT. Experiments show that PRS and SET achieve 2.2× and 4.6× speedup compared to state-of-the-art test methodologies. 
    more » « less
  4. Variability-induced accuracy degradation of RRAMbased DNNs is of great concern due to their significant potential for use in future energy-efficient machine learning architectures. To address this, we propose a two-step process. First, an enhanced testing procedure is used to predict DNN accuracy from a set of compact test stimuli (images). This test response (signature) is simply the concatenated vectors of output neurons of intermediate and final DNN layers over the compact test images applied. DNNs with a predicted accuracy below a threshold are then tuned based on this signature vector. Using a clustering based approach, the signature is mapped to the optimal tuning parameter values of the DNN (determined using off-line training of the DNN via backpropagation) in a single step, eliminating any post-manufacture training of the DNN weights (expensive). The tuning parameters themselves consist of the gains and offsets of the ReLU activation of neurons of the DNN on a per-layer basis and can be tuned digitally. Tuning is achieved in less than a second of tuning time, with yield improvements of over 45% with a modest accuracy reduction of 4% compared to digital DNNs. 
    more » « less
  5. Resistive random access memory (RRAM) based memristive crossbar arrays enable low power and low latency inference for convolutional neural networks (CNNs), making them suitable for deployment in IoT and edge devices. However, RRAM cells within a crossbar suffer from conductance variations, making RRAM-based CNNs vulnerable to degradation of their classification accuracy. To address this, the classification accuracy of RRAM based CNN chips can be estimated using predictive tests, where a trained regressor predicts the accuracy of a CNN chip from the CNN’s response to a compact test dataset. In this research, we present a framework for co-optimizing the pixels of the compact test dataset and the regressor. The novelty of the proposed approach lies in the ability to co-optimize individual image pixels, overcoming barriers posed by the computational complexity of optimizing the large numbers of pixels in an image using state-of-the-art techniques. The co-optimization problem is solved using a three step process: a greedy image downselection followed by backpropagation driven image optimization and regressor fine-tuning. Experiments show that the proposed test approach reduces the CNN classification accuracy prediction error by 31% compared to the state of the art. It is seen that a compact test dataset with only 2-4 images is needed for testing, making the scheme suitable for built-in test applications. 
    more » « less