Self-Tuning Wireless Network Power Management

Current wireless network power management often substantially degrades performance and may even increase overall energy usage when used with latency-sensitive applications. We propose self-tuning power management (STPM) that adapts its behavior to the access patterns and intent of applications, the characteristics of the network interface, and the energy usage of the platform. We have implemented STPM as a Linux kernel module—our results show substantial benefits for distributed file systems, streaming audio, and thin-client applications. Compared to default 802.11b power management, STPM reduces the total energy usage of an iPAQ running the Coda distributed file system by 21% while also reducing interactive file system delay by 80%. Further, STPM adapts to diverse operating conditions: it yields good results on both laptops and handhelds, supports 802.11b network interfaces with substantially different characteristics, and performs well across a range of application network access patterns.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41365/1/11276_2005_Article_1768.pd

Hermes: a Fast, Fault-Tolerant and Linearizable Replication Protocol

Today's datacenter applications are underpinned by datastores that are responsible for providing availability, consistency, and performance. For high availability in the presence of failures, these datastores replicate data across several nodes. This is accomplished with the help of a reliable replication protocol that is responsible for maintaining the replicas strongly-consistent even when faults occur. Strong consistency is preferred to weaker consistency models that cannot guarantee an intuitive behavior for the clients. Furthermore, to accommodate high demand at real-time latencies, datastores must deliver high throughput and low latency. This work introduces Hermes, a broadcast-based reliable replication protocol for in-memory datastores that provides both high throughput and low latency by enabling local reads and fully-concurrent fast writes at all replicas. Hermes couples logical timestamps with cache-coherence-inspired invalidations to guarantee linearizability, avoid write serialization at a centralized ordering point, resolve write conflicts locally at each replica (hence ensuring that writes never abort) and provide fault-tolerance via replayable writes. Our implementation of Hermes over an RDMA-enabled reliable datastore with five replicas shows that Hermes consistently achieves higher throughput than state-of-the-art RDMA-based reliable protocols (ZAB and CRAQ) across all write ratios while also significantly reducing tail latency. At 5% writes, the tail latency of Hermes is 3.6X lower than that of CRAQ and ZAB.Comment: Accepted in ASPLOS 202

Dimethyl fumarate in patients admitted to hospital with COVID-19 (RECOVERY): a randomised, controlled, open-label, platform trial

Dimethyl fumarate (DMF) inhibits inflammasome-mediated inflammation and has been proposed as a treatment for patients hospitalised with COVID-19. This randomised, controlled, open-label platform trial (Randomised Evaluation of COVID-19 Therapy [RECOVERY]), is assessing multiple treatments in patients hospitalised for COVID-19 (NCT04381936, ISRCTN50189673). In this assessment of DMF performed at 27 UK hospitals, adults were randomly allocated (1:1) to either usual standard of care alone or usual standard of care plus DMF. The primary outcome was clinical status on day 5 measured on a seven-point ordinal scale. Secondary outcomes were time to sustained improvement in clinical status, time to discharge, day 5 peripheral blood oxygenation, day 5 C-reactive protein, and improvement in day 10 clinical status. Between 2 March 2021 and 18 November 2021, 713 patients were enroled in the DMF evaluation, of whom 356 were randomly allocated to receive usual care plus DMF, and 357 to usual care alone. 95% of patients received corticosteroids as part of routine care. There was no evidence of a beneficial effect of DMF on clinical status at day 5 (common odds ratio of unfavourable outcome 1.12; 95% CI 0.86-1.47; p = 0.40). There was no significant effect of DMF on any secondary outcome

Speculative Execution Within A Commodity Operating System

For EJN, without whom the journey would never have begun, and for RJN, who is a great part of the reason the journey has completed ii ACKNOWLEDGEMENTS When I arrived at the University of Michigan, Jason Flinn was just getting started as a professor, and I was fortunate enough to become his second graduate student. During our five years working together, Jason’s guidance has been an invaluable asset in conceiving and executing my research. From Jason I learned the art of systems building, and the craft of technical writing. I am grateful to have had him as a mentor. From Peter Chen, with whom I collaborated, I learned the art of refining the rough hewn details of my work into finely tuned principles of research. I am thankful for the opportunity to work with him. I thank my other two committee members, Brian Noble and Ella Atkins. Our discussions about my dissertation and defense provided me with many insights, and helped greatly to improve the final document. I als

Parallelizing security checks on commodity hardware

Speck 1 is a system that accelerates powerful security checks on commodity hardware by executing them in parallel on multiple cores. Speck provides an infrastructure that allows sequential invocations of a particular security check to run in parallel without sacrificing the safety of the system. Speck creates parallelism in two ways. First, Speck decouples a security check from an application by continuing the application, using speculative execution, while the security check executes in parallel on another core. Second, Speck creates parallelism between sequential invocations of a security check by running later checks in parallel with earlier ones. Speck provides a process-level replay system to deterministically and efficiently synchronize state between a security check and the original process. We use Speck to parallelize three security checks: sensitive data analysis, on-access virus scanning, and taint propagation. Running on a 4-core and an 8-core computer, Speck improves performance 4x and 7.5x for the sensitive data analysis check, 3.3x and 2.8x for the on-access virus scanning check, and 1.6x and 2x for the taint propagation check

Energy-efficiency and storage flexibility in the blue file system

A fundamental vision driving pervasive computing research is access to personal and shared data anywhere at anytime. In many ways, this vision is close to being realized. Wireless networks such as 802.11 offer connectivity to small, mobile devices. Portable storage, such as mobile disks and USB keychains, let users carry several gigabytes of data in their pockets. Yet, at least three substantial barriers to pervasive data access remain. First, power-hungry network and storage devices tax the limited battery capacity of mobile computers. Second, the danger of viewing stale data or making inconsistent updates grows as objects are replicated across more computers and portable storage devices. Third, mobile data access performance can suffer due to variable storage access times caused by dynamic power management, mobility, and use of heterogeneous storage devices. To overcome these barriers, we have built a new distributed file system called BlueFS. Compared to the Coda file system, BlueFS reduces file system energy usage by up to 55% and provides up to 3 times faster access to data replicated on portable storage.

Ghosts in the machine: interfaces for better power management

We observe that the modularity of current power management algorithms often leads to poor results. We propose two new interfaces that pierce the abstraction barrier that inhibits device power management. First, an OS power manager allows applications to query the current power mode of I/O devices to evaluate the performance and energy cost of alternative strategies for reading and writing data. Second, we allow applications to disclose ghost hints that enable better power management in the presence of multiple devices. Adaptive applications issue ghost hints to device power managers when they are forced to use a poor I/O path because a device is not in an ideal power mode; such hints allow devices to implement proactive power management strategies that do not depend upon passive load observation. Using these new interfaces, we implement a middleware layer that supports adaptive disk cache management. On an iPAQ handheld running Linux, our cache manager reduces interactive response time for a Web browser by 27 % and decreases total energy usage by 9%. For a mail reader, the cache manager decreases response time by 42 % and energy use by 5%

ABSTRACT Self-Tuning Wireless Network Power Management

Current wireless network power management often substantially degrades performance and may even increase overall energy usage when used with latency-sensitive applications. We propose self-tuning power management (STPM) that adapts its behavior to the access patterns and intent of applications, the characteristics of the network interface, and the energy usage of the platform. We have implemented STPM as a Linux kernel module—our results show substantial benefits for distributed file systems, streaming audio, and thin-client applications. Compared to default 802.11b power management, STPM reduces the total energy usage of an iPAQ running the Coda distributed file system by 21 % while also reducing interactive file system delay by 80%. Further, STPM adapts to diverse operating conditions: it yields good results on both laptops and handhelds, supports 802.11b network interfaces with substantially different characteristics, and performs well across a range of application network access patterns

Virtual ring routing: network routing inspired by DHTs

This paper presents Virtual Ring Routing (VRR), a new network routing protocol that occupies a unique point in the design space. VRR is inspired by overlay routing algorithms in Distributed Hash Tables (DHTs) but it does not rely on an underlying network routing protocol. It is implemented directly on top of the link layer. VRR provides both traditional point-to-point network routing and DHT routing to the node responsible for a hash table key. VRR can be used with any link layer technology but this paper describes a design and several implementations of VRR that are tuned for wireless networks. We evaluate the performance of VRR using simulations and measurements from a sensor network and an 802.11a testbed. The experimental results show that VRR provides robust performance across a wide range of environments and workloads. It performs comparably to, or better than, the best wireless routing protocol in each experiment. VRR performs well because of its unique features: it does not require network flooding or translation between fixed identifiers and location-dependent addresses