R-3 Repository :: Browsing by Author "Zhong, Lin"

Browsing by Author "Zhong, Lin"

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An Empirical Analysis of Internet Use on Smartphones: Characterizing Visit Patterns and User Differences
(2012-09-05) Tossell, Chad; Kortum, Philip; Byrne, Michael D.; Lane, David M.; Zhong, Lin
The original vision of ubiquitous computing was for computers to assist humans by providing subtle and fitting technologies in every environment. The iPhone and similar smartphones have provided continuous access to the internet to this end. In the current thesis, my goal was to characterize how the internet is used on smartphones to better understand what users do with technology away from the desktop. Naturalistic and longitudinal data were collected from iPhone users in the wild and analyzed to develop this understanding. Since there are two general ways to access the internet on smartphones—via native applications and a web browser—I describe usage patterns through each along with the influence of experience, the nature of the task and physical locations where smartphones were used on these patterns. The results reveal differences between technologies (the PC and the smartphone), platforms (native applications and the mobile browser), and users in how the internet was accessed. Findings indicate that longitudinal use of web browsers decreased sharply with time in favor of native application use, web page revisitation through browsers occurred very infrequently (approximately 25% of URLs are revisited by each user), bookmarks were used sparingly to access web content, physical location visitation followed patterns similar to virtual visitation on the internet, and Zipf distributions characterize mobile internet use. The web browser was not as central to smartphone use compared to the PC, but afforded certain types of activities such as searching and ad hoc browsing. In addition, users systematically differed from each other in how they accessed the internet suggesting different ways to support a wider spectrum of smartphone users.
Argos: Practical Base Stations for Large-scale Beamforming
(2012-09-05) Shepard, Clayton; Zhong, Lin; Knightly, Edward W.; Sabharwal, Ashutosh
MU-MIMO theory predicts manyfold capacity gains by leveraging many antennas (e.g. M >> 10) on wireless base stations to serve many users simultaneously through multi-user beamforming (MUBF). However, realizing such a large-scale design is nontrivial, and has yet to be achieved in the real world. We present the design, realization, and evaluation of Argos, the first reported large-scale base station that is capable of serving many (e.g., 10s of) terminals simultaneously through MUBF. Designed with extreme flexibility and scalability in mind, Argos exploits hierarchical and modular design principles, properly partitions baseband processing, and holistically considers real-time requirements of MUBF. To achieve unprecedented scalability, we devise a novel, completely distributed, beamforming technique, as well as an internal calibration procedure to enable implicit beamforming across large arrays. We implement a prototype with 64 antennas, and demonstrate that it can achieve up to 6.7 fold capacity gains while using a mere 1/64th the transmission power.
Argos: Practical Many-Antenna MU-MIMO Systems
(2018-01-09) Shepard, Clayton W; Zhong, Lin
Many-antenna MU-MIMO, or "massive" MIMO at large scale, is a key candidate technology for next-generation wireless systems. However, from a practical design perspective scaling up MU-MIMO presents a number of unique challenges and opportunities. To efficiently utilize computational, power, and channel resources requires a complete redesign of many aspects of traditional MIMO systems, particularly the base station architecture and control channel. Furthermore, mobility fundamentally limits the capacity of many-antenna MU-MIMO systems, thus to efficiently realize practical many-antenna MU-MIMO systems requires performance modeling and testing in real-world environments. This thesis presents a novel scalable many-antenna base station architecture and control channel design, which are implemented and tested on three generations of large-scale custom built hardware platforms. We derive a theoretical model of many-antenna MU-MIMO system performance in real-world environments, accounting for hardware capabilities and channel estimation overhead. Leveraging these many-antenna MU-MIMO platforms, we conducted a comprehensive channel measurement campaign, spanning the UHF, 2.4 GHz, and 5 GHz bands, with varying degrees of mobility. Based on these measurements, we implement a mobility-aware MU-MIMO channel sounding system, which is able to virtually eliminate overhead from unnecessary channel sounding. Combined, these innovations enable many-antenna MU-MIMO systems to be efficiently implemented in real-world environments with mobility.
Automated OS-level Device Runtime Power Management
(2014-12-01) Xu, Chao; Zhong, Lin; Cavallaro, Joseph R; Vardi, Moshe Y; Wallach, Dan S
Hardware devices on a modern System-on-Chip (SoC), ranging from accelerators to IO controllers, usually account for the largest portion of the chip area. It is therefore vital for Operating Systems (OS) to disable and enable these devices at run time, so that idle devices can enter low-power state timely while meeting user’s performance expectation. This is called device runtime Power Management (PM), for which individual device drivers in commodity OSes are held responsible. Based on the observations of existing drivers and their evolution, we consider counting on drivers for device runtime PM harmful. We identify three pieces of information essential to device runtime PM, and show that all of them can be obtained without involving drivers, either by using a software inference approach atop existing ARM-based SoC, or more efficiently, by adding one register bit to each device. We thus argue for a structural change to the current Linux runtime PM framework, replacing PM code in each individual driver with one kernel module called central PM agent. We experimentally show that central PM agent is just as effective as hand-tuned driver PM code. We also present a software tool called PowerAdvisor, as a remedy to simplify driver PM efforts without overhauling the current Linux runtime PM framework. PowerAdvisor analyzes trace generated from historic executions and suggests PM calls to be inserted at certain driver source locations. Although a best-effort tool, PowerAdvisor not only reproduces hand-tuned PM code that already exists in stock drivers, but also correctly suggests PM code never known before . Overall, our experiences show that it is promising to ultimately free driver developers from manual PM.
Beamforming on Mobile Devices: A First Study
(2011) Yu, Hang; Zhong, Lin
In this work, we report the first study of beamforming on mobile devices. We first show that beamforming is already feasible on mobile devices in terms of form factor, power efficiency and device mobility. We then investigate the optimal way of using beamforming in terms of power efficiency, by allowing a dynamic number of active antennas. We propose a simple yet effective solution, BeamAdapt, which allows each mobile client in a network to iteratively identify the optimal number of active antennas with fast convergence and close-to-optimal performance. Finally we report a WARP-based prototype of BeamAdapt and experimentally demonstrate its effectiveness in realistic environments. We also complement the prototype-based experiments with Qualnet-based simulation of a large-scale network. Our results show that BeamAdapt with four antennas can reduce the power consumption of mobile clients by more than half compared to omni directional transmission, while maintaining a required network throughput.
BeamSwitch: System solution for energy-efficient directional communication on mobile devices
(2010) Dumanli, Hasan Huseyin; Zhong, Lin
Directional communication has the potential to improve both the energy efficiency of wireless communication without sacrificing its quality. We present a system solution, BeamSwitch, for directional communication on mobile devices. BeamSwitch employs a special multi-antenna system that consists of multiple identical directional antenna or beams, a single regular omni antenna, and a single RF chain. It uses one of the directional beams for transmitting data frames and receiving their acknowledgments and the regular antenna for all other transceiving. BeamSwitch tracks the signal strength of incoming frames and selects the right beam for data transmission. We report an extensive evaluation of BeamSwitch including both measurements with a prototype with three beams and Qualnet-based simulation. Our evaluation shows that BeamSwitch with three 6 dBi directional antennas can improve the energy efficiency of a commercial 802.11 adapter by over 20% and simultaneously provide better or close communication quality. BeamSwitch achieves this under diverse radio propagation environments and extreme mobility (up to 360° per second direction change).
Client Beamforming for Rate Scalability of MU-MIMO Networks
(2015-04-24) Yu, Hang; Zhong, Lin; Knightly, Edward W; Sabharwal, Ashutosh; Johnson, David B
The multi-user MIMO (MU-MIMO) technology allows an AP with multiple antennas to simultaneously serve multiple clients to improve the network capacity. To achieve this, the AP leverages zero-forcing beamforming (ZFBF) to eliminate the intra-cell interference between served clients. However, current MU-MIMO networks suffer from two fundamental problems that limit the network capacity. First, for a single MU-MIMO cell, as the number of clients approaches the number of antennas on the AP, the cell capacity often flattens and may even drop. Second, for multiple MU-MIMO cells, the multiple APs cannot simultaneously serve their clients due to inter-cell interference, so that the concurrent streams are constrained to a single cell with limited network capacity. Our unique perspective to tackle these two problems is that modern mobile clients can be equipped with multiple antennas for beamforming. We have proposed two solutions that leverage the client antennas. For the capacity scalability problem in a single MU-MIMO cell, we use multiple client antennas to improve the orthogonality between the channel vectors of the clients. The orthogonality between clients’ channels determines the SNR reduction from the zero-forcing beamforming by the AP, and is therefore critical for the capacity of a MU-MIMO cell to become more scalable to the number of clients. We have devised a 802.11ac-based protocol called MACCO, in which each client locally optimizes its beamforming weights based on the channel knowledge obtained from overhearing other clients’ channel reports. For the inter-cell interference problem in multiple MU-MIMO cells, we leverage multiple client antennas to assist the interfering APs to coordinately cancel the inter-cell interference between them. To achieve such coordinated interference cancellation in a practical way, We have proposed a two-step optimization including antenna usage optimization and beamforming weight optimization. We have devised another 802.11ac-based protocol called CoaCa, which integrates this two-step optimization into 802.11ac with small modifications and negligible overhead, allowing each AP and client to locally identify the optimal beamforming weights. We have implemented both MACCO and CoaCa on the WARP SDR platform leveraging the WARPLab framework, and experimentally evaluated their performance under real-world indoor wireless channels. The results have demonstrated the effectiveness of MACCO and CoaCa toward solving the capacity scalability and inter-cell interference problems of MU-MIMO networks. First, on average MACCO can increase the capacity of a single MU-MIMO cell with eight AP antennas and eight clients by 35%, compared to existing solutions that use client antennas differently. Second, for a MU-MIMO network with two cells, by cancelling the inter-cell interference CoaCa can convert the majority of the number of streams increase (50%-67%) into network capacity improvement (41%-52%).
Context for system resource management: An application in wireless data management
(2008) Rahmati, Ahmad; Zhong, Lin
Context information brings new opportunities for efficient and effective system resource management of mobile devices. In this work, we focus on the use of context information to manage wireless data. The findings from our field-collected data show that the energy cost of network interfaces poses a great challenge to ubiquitous connectivity, despite fairly good network availability. Based on our findings, we propose to leverage the complementary strengths of Wi-Fi and cellular networks by automatically selecting the more energy-efficient wireless interface based on context information. We formulate the selection of wireless interfaces as a statistical decision problem. The key challenge is to accurately estimate Wi-Fi network conditions without powering up its network interface. We explore the use of different context information, including time, history, cellular network conditions, and device motion, and devise algorithms that can effectively learn from context information and estimate the probability distribution of Wi-Fi network conditions. Simulations based on field-collected traces show that our algorithms can improve the average battery lifetime of a commercial mobile phone for a three-channel ECG reporting application by 39%, very close to the determined theoretical upper bound of 42%. Finally, a field validation of our most simple algorithm demonstrates a 35% battery lifetime improvement in normal usage.
Context in Mobile System Design: Characterization, Theory, and Implications
(2012-09-05) Rahmati, Ahmad; Zhong, Lin; Knightly, Edward W.; Sabharwal, Ashutosh; Kortum, Philip
Context information brings new opportunities for efficient and effective applications and services on mobile devices. Many existing work exploit the context dependency of mobile usage for specific applications, and show significant, quantified, performance gains by utilizing context. In order to be practical, such works often pay careful attention to the energy and processing costs of context awareness while attempting to maintain reasonable accuracy. These works also have to deal with the challenges of multiple sources of context, which can lead to a sparse training data set. Even with the abundance of such work, quantifying context-dependency and the relationship between context-dependency and performance achievements remains an open problem, and solutions to manage the and challenges of context awareness remain ad-hoc. To this end, this dissertation methodologically quantifies and measures the context dependency of three principal types of mobile usage in a methodological, application agnostic yet practical manner. The three usages are the websites the user visits, the phone numbers they call, and the apps they use, either built-in or obtained by the user from the App Store . While this dissertation measures the context dependency of these three principal types of mobile usage, its methodology can be readily extended to other context-dependent mobile usage and system resources. This dissertation further presents SmartContext, a framework to systematically optimize the energy cost of context awareness by selecting among different context sources, while satisfying the system designer’s cost-accuracy tradeoffs. Finally, this thesis investigates the collective effect of social context on mobile usage, by separating and comparing LiveLab users based on their socioeconomic groups. The analysis and findings are based on usage and context traces collected in real-life settings from 24 iPhone users over a period of one year. This dissertation presents findings regarding the context dependency of three principal types of mobile usage; visited websites, phone calls, and app usage. The methodology and lessons presented here can be readily extended to other forms of context and context-dependent usage and resources. They guide the development of context aware systems, and highlight the challenges and expectations regarding the context dependency of mobile usage.
Controlling Race Conditions in OpenFlow to Accelerate Application Verification and Packet Forwarding
(2014-10-24) Sun, Xiaoye Steven; Ng, T. S. Eugene; Knightly, Edward W; Zhong, Lin
OpenFlow is a Software Defined Networking (SDN) protocol that is being deployed in critical network systems. SDN application verification takes an important role in guaranteeing the correctness of the application. Through our investigation, we discover that application verification can be very inefficient under the OpenFlow protocol since there are many race conditions between the data packets and control plane messages. Furthermore, these race conditions also increase the control plane workload and packet forwarding delay. We propose Attendre, an OpenFlow extension, to mitigate the ill effects of the race conditions in OpenFlow networks. We have implemented Attendre in NICE (a model checking verifier), Open vSwitch (a software virtual switch) and NOX (an OpenFlow control platform). Experiments show that Attendre can reduce verification time by several orders of magnitude, and can significantly reduce TCP connection setup time.
Cooperative Execution of Parallel Tasks with Synchronization Constraints
(2015-10-14) Imam, Shams Mahmood; Sarkar, Vivek; Mellor-Crummey, John; Chaudhuri, Swarat; Zhong, Lin
The topic of this thesis is the effective execution of parallel applications on emerging multicore and manycore systems in the presence of modern synchronization and coordination constraints. Synchronization and coordination can contribute significant productivity and performance overheads to the development and execution of parallel programs. Higher-level programming models, such as the Task Parallel Model and Actor Model, provide abstractions that can be used to simplify writing parallel programs, in contrast to lower-level programming models that directly expose locks, threads and processes. However, these higher-level models often lack efficient support for general synchronization patterns that are necessary for a wide range of applications. Many modern synchronization and coordination constructs in parallel programs can incur significant performance overheads on current runtime systems, or significant productivity overheads when the programmer is forced to complicate their code to mitigate these performance overheads. We believe that a cooperation between the programmer and the runtime system is necessary to reduce the parallel overhead and to execute the available parallelism efficiently in the presence of synchronization constraints. In a cooperative approach, an executing entity yields control to other entities at well-defined points during its execution. This thesis shows that the use of cooperative techniques is critical to performance and scalability of certain parallel programming models, especially in the presence of modern synchronization and coordination constraints such as asynchronous tasks, futures, phasers, data-driven tasks, and actors. In particular, we focus on cooperative extensions and runtimes for the async-finish Task Parallel Model and the Actor Model in this thesis. Our work shows that cooperative techniques simplify programmability and deliver significant performance improvements by reducing the overhead in modern parallel programming models.
Design and Implementation of I/O Servers Using the Device File Boundary
(2015-07-31) Amiri Sani, Ardalan; Zhong, Lin; Varman, Peter; Wallach, Dan; Vasudevan, Venu
Due to historical reasons, today's computer systems treat I/O devices as second-class citizens, supporting them with ad hoc and poorly-developed system software. As I/O devices are getting more diverse and are taking a central role in modern systems from mobile systems to servers, such second-class system support hinders novel system services such as I/O virtualization and sharing. The goal of this thesis is to tackle these challenges by rethinking the system support for I/O devices. For years, research for I/O devices is limited largely to network and storage devices. However, a diverse set of I/O devices are increasingly important for emerging computing paradigms. For modern mobile systems such as smartphones and tablets, I/O devices such as sensors and actuators are essential to the user experience. At the same time, high-performance computers in datacenters are embracing hardware specialization, or accelerators, such as GPU, DSP, crypto accelerator, etc., to improve the system performance and efficiency as the Dennard scaling has ended. Modern systems also treat such specialized hardware as I/O devices. Since I/O devices are becoming the fundamental service provided by many computer systems, we suggest that they should be treated as I/O servers that are securely accessible to other computers, i.e., clients, as well. I/O servers will be the fundamental building blocks of future systems, enabling the novel system services mentioned above. For example, they enable a video chat application running on a tablet to use the camera on the user's smart glasses and, for better consolidation, enable all applications running in a datacenter to share an accelerator cluster over the network. We address two fundamental challenges of I/O servers: remote access and secure sharing. Remote access enables an application in one machine, either virtual or physical, to use an I/O device in a different machine. We use a novel boundary for remote access: Unix device files, which are used in Unix-like operating systems to abstract various I/O devices. Using the device file boundary for remote access requires low engineering effort as it is common to many classes of I/O devices. In addition, we show that this boundary achieves high performance, supports legacy applications and I/O devices, supports multiple clients, and makes all features of I/O devices available to unmodified applications. An I/O server must provide security guarantees for untrusting clients. Using the device file boundary, a malicious client can exploit the -- very common -- security bugs in device drivers to compromise the I/O server and hence other clients. We propose two solutions for this problem. First, if available in the I/O server, we use a trusted hypervisor to enforce fault and device data isolation between clients. This solution assumes the driver is compromised and hence cannot guarantee functional correctness. Therefore, as a second solution, we present a novel device driver design, called library drivers, that minimizes the device driver Trusted Computing Base (TCB) size and attack surface and hence reduces the possibility of the driver-based exploits. Using our solutions for remote access and secure sharing, we demonstrate that I/O servers enable novel system services: (i) I/O sharing between virtual machines, i.e., I/O virtualization, where virtual machines (VMs) share the I/O devices in the underlying physical machine, (ii) I/O sharing between mobile systems, where one mobile system uses the I/O devices of another system over a wireless connection, and (iii) I/O sharing between servers in a datacenter, where the VMs in one server use the I/O devices of other servers over the network.
Design Space Exploration of Parallel Algorithms and Architectures for Wireless Communication and Mobile Computing Systems
(2014-10-30) Wang, Guohui; Cavallaro, Joseph R.; Sarkar, Vivek; Zhong, Lin; Juntti, Markku
During past several years, there has been a trend that the modern mobile SoC (system-on-chip) chipsets start to incorporate in one single chip the functionality of several general purpose processors and application-specific accelerators to reduce the cost, the power consumption and the communication overhead. Given the ever-growing performance requirements and strict power constraints, the existence of different types of signal processing workloads have posed challenges to the mapping of the computationally-intensive algorithms to the heterogeneous architecture of the mobile SoCs. Many such signal processing workloads such as channel decoding for wireless communication modem and mobile computer vision applications have high computational complexity, which requires accelerators implemented with parallel algorithms and architectures to meet the performance requirements. Partitioning the workloads and deploying them with the appropriate components of mobile chipsets are crucial to fully utilize the mobile SoC's heterogeneous architecture. The goal of this thesis is to study parallel algorithms and architecture of high performance signal processing accelerators for several representative application workloads in wireless communication and mobile computing systems. We explore the design space of the parallel algorithms and architectures and highlight the workload partitioning and architecture-aware optimization schemes including algorithmic optimization, data structure optimization, and memory access optimization to improve the throughput performance and hardware (or energy) efficiency. As case studies, we will first propose contention-free interleaver architecture for parallel turbo decoding, which enables high throughput multi-standard turbo decoding ASIC (application-specific integrated circuit) with efficient hardware. Secondly, we propose massively parallel LDPC (low-density parity-check) decoding algorithm and implementation using GPU (graphics processor unit), which leads to high throughput and low latency LDPC decoding for practical SDR (software-defined radio) systems. Furthermore, we take advantage of the heterogeneous mobile CPU and GPU to accelerate representative mobile computer vision algorithms such as image editing and local feature extraction algorithms. Based on algorithm analysis and experimental results from the above case studies, we finally explore the design space and compare the performance of accelerator architectures for wireless communication and mobile vision use cases. We will show that the heterogeneous architecture of mobile systems is the key to efficiently accelerating parallel algorithms in order to meet the growing requirements of performance, efficiency, and flexibility.
Detecting Events From Twitter In Real-Time
(2013-09-16) Zhao, Siqi; Zhong, Lin; Sabharwal, Ashutosh; Subramanian, Devika; Vasuderan, Venu
Twitter is one of the most popular online social networking sites. It provides a unique and novel venue of publishing: it has over 500 million active users around the globe; tweets are brief, limited to 140 characters, an ideal way for people to publish spontaneously. As a result, Twitter has the short delays in reflecting what its users perceive, compared to other venues such as blogs and product reviews. We design and implement SportSense, which exploits Twitter users as human sensors of the physical world to detect major events in real-time. Using the National Football League (NFL) games as a targeted domain, we report in-depth studies of the delay and trend of tweets, and their dependence on other properties. We present event detection method based on these findings, and demonstrate that it can effectively and accurately extract major game events using open access Twitter data. SportSense has been evolving during the 2010-11 and 2011-12 NFL seasons and it has been collecting hundreds of millions tweets. We provide SportSense API for developers to use our system to create Twitter-enabled applications.
Directional Antenna Diversity for Mobile Devices: Characterizations and Solutions
(2011) Amiri Sani, Ardalan; Zhong, Lin
We report a first-of-its-kind realization of directional transmission for smartphone-like mobile devices using multiple passive directional antennas, supported by only one RF chain. The key is a multi-antenna system (MiDAS) and its antenna selection methods that judiciously select the right antenna for transmission. It is grounded by two measurementdriven studies regarding 1) how smartphones rotate during wireless usage in the field and 2) how orientation and rotation impact the performance of directional antennas under various propagation environments. We implement MiDAS using the WARP platform, and evaluate it usmg a computerized motor to rotate the prototype according to traces collected from smartphone users in the field. Our evaluation shows MiDAS achieves median of 3dB increase in link gain. Combined with rate adaptation and power control, MiDAS also improves goodput and power saving. MiDAS does not require any changes to the network infrastructure, and is therefore suitable for immediate deployment.
Dual Wi-Fi: Dual Channel Wi-Fi for Congested WLANs with Asymmetric Traffic Loads
(2013-10-08) Flores Miranda, Adriana; Knightly, Edward W.; Sabharwal, Ashutosh; Zhong, Lin
In many WLANs scenarios, the load transmitted from the AP to the clients (Downlink), far outweighs traffic demand from the clients to the AP (Uplink), thereby yielding traffic asymmetry. Moreover, when many clients associate with a single AP, the clients can cause a disproportional amount of medium contention compared to the AP, producing contention asymmetry. We present Dual Wi-Fi, a MAC architecture and protocol that minimizes MAC overhead by matching spectrum resources to traffic asymmetry. Dual Wi-Fi separates uplink and downlink data traffic into two variable-width independent channels, each allocated in accordance to the network's traffic demand. Our experimental and simulation results demonstrate that Dual Wi-Fi matches downlink vs. uplink throughput ratio to demand ratio within 1\% under any client density and traffic load. Through this matching capability, Dual Wi-Fi offers unbounded downlink gains as congestion increases, minimizing and in some cases eliminating retransmissions and contention time.
Dynamic Data Race Detection for Structured Parallelism
(2013-07-24) Raman, Raghavan; Sarkar, Vivek; Mellor-Crummey, John; Zhong, Lin
With the advent of multicore processors and an increased emphasis on parallel computing, parallel programming has become a fundamental requirement for achieving available performance. Parallel programming is inherently hard because, to reason about the correctness of a parallel program, programmers have to consider large numbers of interleavings of statements in different threads in the program. Though structured parallelism imposes some restrictions on the programmer, it is an attractive approach because it provides useful guarantees such as deadlock-freedom. However, data races remain a challenging source of bugs in parallel programs. Data races may occur only in few of the possible schedules of a parallel program, thereby making them extremely hard to detect, reproduce, and correct. In the past, dynamic data race detection algorithms have suffered from at least one of the following limitations: some algorithms have a worst-case linear space and time overhead, some algorithms are dependent on a specific scheduling technique, some algorithms generate false positives and false negatives, some have no empirical evaluation as yet, and some require sequential execution of the parallel program. In this thesis, we introduce dynamic data race detection algorithms for structured parallel programs that overcome past limitations. We present a race detection algorithm called ESP-bags that requires the input program to be executed sequentially and another algorithm called SPD3 that can execute the program in parallel. While the ESP-bags algorithm addresses all the above mentioned limitations except sequential execution, the SPD3 algorithm addresses the issue of sequential execution by scaling well across highly parallel shared memory multiprocessors. Our algorithms incur constant space overhead per memory location and time overhead that is independent of the number of processors on which the programs execute. Our race detection algorithms support a rich set of parallel constructs (including async, finish, isolated, and future) that are found in languages such as HJ, X10, and Cilk. Our algorithms for async, finish, and future are precise and sound for a given input. In the presence of isolated, our algorithms are precise but not sound. Our experiments show that our algorithms (for async, finish, and isolated) perform well in practice, incurring an average slowdown of under 3x over the original execution time on a suite of 15 benchmarks. SPD3 is the first practical dynamic race detection algorithm for async-finish parallel programs that can execute the input program in parallel and use constant space per memory location. This takes us closer to our goal of building dynamic data race detectors that can be "always-on" when developing parallel applications.
Electronic devices containing switchably conductive silicon oxides as a switching element and methods for production and use thereof
(2013-11-26) Tour, James M.; Yao, Jun; Natelson, Douglas; Zhong, Lin; He, Tao; Rice University; United States Patent and Trademark Office
In various embodiments, electronic devices containing switchably conductive silicon oxide as a switching element are described herein. The electronic devices are two-terminal devices containing a first electrical contact and a second electrical contact in which at least one of the first electrical contact or the second electrical contact is deposed on a substrate to define a gap region therebetween. A switching layer containing a switchably conductive silicon oxide resides in the gap region between the first electrical contact and the second electrical contact. The electronic devices exhibit hysteretic current versus voltage properties, enabling their use in switching and memory applications. Methods for configuring, operating and constructing the electronic devices are also presented herein.
Electronic devices containing switchably conductive silicon oxides as a switching element and methods for production and use thereof
(2015-09-08) Tour, James M.; Yao, Jun; Natelson, Douglas; Zhong, Lin; He, Tao; Rice University; United States Patent and Trademark Office
In various embodiments, electronic devices containing switchably conductive silicon oxide as a switching element are described herein. The electronic devices are two-terminal devices containing a first electrical contact and a second electrical contact in which at least one of the first electrical contact or the second electrical contact is deposed on a substrate to define a gap region therebetween. A switching layer containing a switchably conductive silicon oxide resides in the gap region between the first electrical contact and the second electrical contact. The electronic devices exhibit hysteretic current versus voltage properties, enabling their use in switching and memory applications. Methods for configuring, operating and constructing the electronic devices are also presented herein.
Energy Accounting and Optimization for Mobile Systems
(2013-09-16) Dong, Mian; Zhong, Lin; Cavallaro, Joseph R.; Varman, Peter J.; Sarkar, Vivek
Energy accounting determines how much a software process contributes to the total system energy consumption. It is the foundation for evaluating software and has been widely used by operating system based energy management. While various energy accounting policies have been tried, there is no known way to evaluate them directly simply because it is hard to track every hardware use by software in a heterogeneous multicore system like modern smartphones and tablets. This work provides the ground truth for energy accounting based on multi-player game theory and offers the first evaluation of existing energy accounting policies, revealing their important flaws. The proposed ground truth is based on Shapley value, a single value solution to multi-player games of which four axiomatic properties are natural and self-evident to energy accounting. This work further provides a utility optimization formulation of energy management and shows, surprisingly, that energy accounting does not matter for existing energy management solutions that control the energy use of a process by giving it an energy budget, or budget based energy management (BEM). This work shows an optimal energy management (OEM) framework can always outperform BEM. While OEM does not require any form of energy accounting, it is related to Shapley value in that both require the system energy consumption for all possible combination of processes under question. This work reports a prototype implementation of both Shapley value-based energy accounting and OEM based scheduling. Using this prototype and smartphone workload, this work experimentally demonstrates how erroneous existing energy accounting policies can be, show that existing BEM solutions are unnecessarily complicated yet underperforming by 20% compared to OEM.

Browsing by Author "Zhong, Lin"

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