Networked sensors and actuators are increasingly permeating our computing devices, and provide a variety of functions for Internet of Things (IoT) devices and applications. However, this sensor data can also be used by applications to extract private information about users. Applications and users are thus in a tussle over access to private data. Tussles occur in operating systems when stakeholders with competing interests try to access shared resources such as sensor data, CPU time, or network bandwidth. Unfortunately, existing operating systems lack a principled approach for identifying, tracking, and resolving such tussles. Moreover, users typically have little control over how tussles are resolved. Controls for sensor data tussles, for example, often fail to address trade-offs between functionality and privacy. Therefore, we propose a framework to explicitly recognize and manage tussles. Using sensor data as an example resource, we investigate the design of mechanisms for detecting and resolving privacy tussles in a cyber-physical system, enabling privacy and functionality to be negotiated between users and applications. In doing so, we identify shortcomings of existing research and present directions for future work.

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Most video streaming traffic is delivered over HTTP using standard web servers. While traditional web server workloads consist of requests that are primarily for small files that can be serviced from the file system cache, HTTP video streaming workloads often service a long tail of large infrequently requested videos. As a result, optimizing disk accesses is critical to obtaining good server throughput. In this article we explore serialized, aggressive disk prefetching, a technique that can be used to improve the throughput of HTTP streaming video web servers. We identify how serialization and aggressive prefetching affect performance, and, based on our findings, we construct and evaluate Libception, an application-level shim library that implements both techniques. By dynamically linking against Libception at runtime, applications are able to transparently obtain benefits from serialization and aggressive prefetching without needing to change their source code. In contrast to other approaches that modify applications, make kernel changes, or attempt to optimize kernel tuning, Libception provides a portable and relatively simple system in which techniques for optimizing I/O in HTTP video streaming servers can be implemented and evaluated. We empirically evaluate the efficacy of serialization and aggressive prefetching both with and without Libception, using three web servers (Apache, nginx, and the userver) running on two operating systems (FreeBSD and Linux). We find that, by using Libception, we can improve streaming throughput for all three web servers by at least a factor of 2 on FreeBSD and a factor of 2.5 on Linux. Additionally, we find that with significant tuning of Linux kernel parameters, we can achieve similar performance to Libception by globally modifying Linux’s disk prefetch behaviour. Finally, we demonstrate Libception’s ability to reduce the completion time of a microbenchmark involving two applications competing for disk resources.

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