We are Going to the Space -- Part 1: Which device to deploy in a satellite?

The shrinkage in sizes of components that make up satellites led to wider and low cost availability of satellites. As a result, there has been an advent of smaller organizations having the ability to deploy satellites with a variety of data-intensive applications to run on them. One popular application is image analysis to detect, for example, land, ice, clouds, etc. However, the resource-constrained nature of the devices deployed in satellites creates additional challenges for this resource-intensive application. In this paper, we investigate the performance of a variety of edge devices for deep-learning-based image processing in space. Our goal is to determine the devices that satisfy the latency and power constraints of satellites while achieving reasonably accurate results. Our results demonstrate that hardware accelerators (TPUs, GPUs) are necessary to reach the latency requirements. On the other hand, state-of-the-art edge devices with GPUs could have a high power draw, making them unsuitable for deployment on a satellite.

Deep Learning Training on Multi-Instance GPUs

Deep learning training is an expensive process that extensively uses GPUs, but not all model training saturates the modern powerful GPUs. Multi-Instance GPU (MIG) is a new technology introduced by NVIDIA that can partition a GPU to better fit workloads that don't require all the memory and compute resources of a full GPU. In this paper, we examine the performance of a MIG-enabled A100 GPU under deep learning workloads of three sizes focusing on image recognition training with ResNet models. We investigate the behavior of these workloads when running in isolation on a variety of MIG instances allowed by the GPU in addition to running them in parallel on homogeneous instances co-located on the same GPU. Our results demonstrate that employing MIG can significantly improve the utilization of the GPU when the workload is too small to utilize the whole GPU in isolation. By training multiple small models in parallel, more work can be performed by the GPU per unit of time, despite the increase in time-per-epoch, leading to $\sim$3 times the throughput. In contrast, for medium and large-sized workloads, which already utilize the whole GPU well on their own, MIG only provides marginal performance improvements. Nevertheless, we observe that training models in parallel using separate MIG partitions does not exhibit interference underlining the value of having a functionality like MIG on modern GPUs.

Micro-architectural Analysis of a Learned Index

Since the publication of The Case for Learned Index Structures in 2018, there has been a rise in research that focuses on learned indexes for different domains and with different functionalities. While the effectiveness of learned indexes as an alternative to traditional index structures such as B+Trees have already been demonstrated by several studies, previous work tend to focus on higher-level performance metrics such as throughput and index size. In this paper, our goal is to dig deeper and investigate how learned indexes behave at a micro-architectural level compared to traditional indexes. More specifically, we focus on previously proposed learned index structure ALEX, which is a tree-based in-memory index structure that consists of a hierarchy of machine learned models. Unlike the original proposal for learned indexes, ALEX is designed from the ground up to allow updates and inserts. Therefore, it enables more dynamic workloads using learned indexes. In this work, we perform a micro-architectural analysis of ALEX and compare its behavior to the tree-based index structures that are not based on learned models, i.e., ART and B+Tree. Our results show that ALEX is bound by memory stalls, mainly stalls due to data misses from the last-level cache. Compared to ART and B+Tree, ALEX exhibits fewer stalls and a lower cycles-per-instruction value across different workloads. On the other hand, the amount of instructions required to handle out-of-bound inserts in ALEX can increase the instructions needed per request significantly (10X) for write-heavy workloads. However, the micro-architectural behavior shows that this increase in the instruction footprint exhibit high instruction-level parallelism, and, therefore, does not negatively impact the overall execution time.