B-LOG: A branch and bound methodology for the parallel execution of logic programs

We propose a computational methodology -"B-LOG"-, which offers the potential for an effective implementation of Logic Programming in a parallel computer. We also propose a weighting scheme to guide the search process through the graph and we apply the concepts of parallel "branch and bound" algorithms in order to perform a "best-first" search using an information theoretic bound. The concept of "session" is used to speed up the search process in a succession of similar queries. Within a session, we strongly modify the bounds in a local database, while bounds kept in a global database are weakly modified to provide a better initial condition for other sessions. We also propose an implementation scheme based on a database machine using "semantic paging", and the "B-LOG processor" based on a scoreboard driven controller

Study of the modifications needed for effective operation NASTRAN on IBM virtual storage computers

The necessary modifications were determined to make NASTRAN operational under virtual storage operating systems (VS1 and VS2). Suggested changes are presented which will make NASTRAN operate more efficiently under these systems. Estimates of the cost and time involved in design, coding, and implementation of all suggested modifications are included

zCap: a zero configuration adaptive paging and mobility management mechanism

Today, cellular networks rely on fixed collections of cells (tracking areas) for user equipment localisation. Locating users within these areas involves broadcast search (paging), which consumes radio bandwidth but reduces the user equipment signalling required for mobility management. Tracking areas are today manually configured, hard to adapt to local mobility and influence the load on several key resources in the network. We propose a decentralised and self-adaptive approach to mobility management based on a probabilistic model of local mobility. By estimating the parameters of this model from observations of user mobility collected online, we obtain a dynamic model from which we construct local neighbourhoods of cells where we are most likely to locate user equipment. We propose to replace the static tracking areas of current systems with neighbourhoods local to each cell. The model is also used to derive a multi-phase paging scheme, where the division of neighbourhood cells into consecutive phases balances response times and paging cost. The complete mechanism requires no manual tracking area configuration and performs localisation efficiently in terms of signalling and response times. Detailed simulations show that significant potential gains in localisation effi- ciency are possible while eliminating manual configuration of mobility management parameters. Variants of the proposal can be implemented within current (LTE) standards

Analysis of some algorithms for use on paged virtual memory computers

PhD ThesisHandling a single page fault involves execution of thousands of instructions, drum rotational delay and is usually so expensive that if it can be avoided, almost any other cost can be tolerated. Optimizing operating system performance is usually the main concern of computer seientists who deal with paged memories. However, redesigning the algorithm used by a problem program can often result in a very significant reduction in paging, and hence in program execution time. The redesigned algorithm frequently does not satisfy the more conventional efficiency criteria. A sorting algorithm, Hash Coding and other search algorithms are considered. Analytic and simulation studies are presented, and aome modifications are proposed to reduce the number of page faults produced by data set references. Analysis is in terms of three of the most commonly used page replacement algorithms i.e. least recently used, first in first out, and random selection. The modifications are for the most part relatively minor and in some cases have appeared elsewhere in the context of searching on external storage media. The important aspects are the dramatic performance improvements which are possible, and the fact that classical internal algorithms are inappropriate for use in a paged virtual memory system.The Science Research Council: The University of Newcastle Upon Tyne: International Business Machines (United Kingdom) Limited.

Effect of screen presentation on text reading and revising. International Journal of Human-Computer Studies

Two studies using the methods of experimental psychology assessed the effects of two types of text presentation (page-by-page vs. scrolling) on participants' performance while reading and revising texts. Greater facilitative effects of the page-by-page presentation were observed in both tasks. The participants' reading task performance indicated that they built a better mental representation of the text as a whole and were better at locating relevant information and remembering the main ideas. Their revising task performance indicated a larger number of global corrections (which are the most difficult to make)

UTILISING NETWORKED WORKSTATIONS TO ACCELERATE DATABASE QUERIES

The rapid growth in the size of databases and the advances made in Query Languages has resulted in increased SQL query complexity submitted by users, which in turn slows down the speed of information retrieval from the database. The future of high performance database systems lies in parallelism. Commercial vendors´ database systems have introduced solutions but these have proved to be extremely expensive. This paper investagetes how networked resources such as workstations can be utilised by using Parallel Virtual Machine (PVM) to Optimise Database Query Execution. An investigation and experiments of the scalability of the PVM are conducted. PVM is used to implement palallelism in two separate ways: (i) Removes the work load for deriving and maintaining rules from the data server for Semantic Query Optimisation, therefore clears the way for more widespread use of SQO in databases [16], [5]. (ii) Answers users queries by a proposed Parallel Query Algorithm PQA which works over a network of workstations, coupled with a sequential Database Management System DBMS called PostgreSql on the prototype called Expandable Server Architecture ESA [11], [12], [21], [13]. Experiments have been conducted to tackle the problems of Parallel and Distributed systems such as task scheduling, load balance and fault tolerance

가상화 환경을 위한 원격 메모리

학위논문(박사) -- 서울대학교대학원 : 공과대학 전기·컴퓨터공학부, 2021.8. Bernhard Egger.클라우드 환경은 거대한 연산 자원을 상시 가동할 필요 없고 원하는 순간 원하는 양의 대한 연산 비용만을 지불하면 되기 때문에, 최근 인공지능 및 빅데이터 연산의 유행으로 인해 그 수요가 크게 증가하고 있다. 이러한 클라우드 컴퓨팅의 도입으로인해 고객은 서버 유지에 대한 비용을 크게 절감할 수 있고 서비스 제공자는 연산 자원의 이용 효율을 극대화 할 수 있다. 이러한 시나리오에서 데이터센터 입장에서는 연산 자원 활용 효율을 개선하는 것이 중요한 목표가 된다. 특히 최근 폭증하고 있는 데이터 센터의 규모를 고려하면 작은 효율 개선으로도 막대한 경제적 가치를 창출 할 수 있다. 데이터 센터의 효율은 위치 선정, 구조 설계, 냉각 시스템, 하드웨어 구성 등등 다양한 요소들에 영향을 받지만, 이 논문에서는 특히 연산 및 메모리 자원을 관리하는 소프트웨어 설계 및 구현을 다룬다. 본 논문에서는 데이터 센터 효율 개선을 획기적으로 개선하는 두가지 소프트웨어 기반 기술을 제안한다. 첫 째로 가상화 환경을 위한 소프트웨어 기반 메모리 분리 시스템을 제안한다. 최근 고속 네트워크의 발전으로 인해 원격 메모리 접근 비용이 획기적으로 줄어 들었고, 이 논문에서는 고성능 네트워킹 하드웨어를 이용하여 원격 메모리 위에서 실행되는 가상 머신의 큰 성능 저하 없이 실행할 수 있음을 보인다. 제안된 기술을 QEMU/KVM 가상머신 하이퍼바이저를 통해 평가한 결과, 본 논문에서 제안한 기법은 기존 시스템 대비 원격 페이징에 대한 꼬리 지연시간을 98.2% 개선함을 보인다. 또한 랙 규모의 작업처리 시뮬레이션을 통한 실험에서, 제안된 시스템은 전체 작업 처리 시간을 기존 시스템 대비 40.9% 줄일 수 있음을 보인다. 두 번째로 원격 메모리를 이용하는 즉각적인 가상머신 이주 기법을 제안하다. 가상화 환경의 원격 메모리 활용에 대한 확장은 그것만으로 자원 이용률 향상에 대해 큰 기여를 하지만, 여전히 한 서버에서 여러 어플리케이션이 경쟁적으로 자원을 이용하는 경우 성능이 크게 저하 될 수 있다. 이 논문에서 제안하는 즉각적인 가상머신 이주 기법은 원격 메모리 상에서 아주 작은 메타데이터의 전송만으로 가상머신의 이주를 가능하게 하며, 메모리 상에 키와 값을 저장하는 데이터베이스 벤치마크를 실행하는 가상머신을 기반으로 한 평가에서 기존 기법대비 실질적인 서비스 중단시간을 최대 92.6% 개선함을 보인다.The raising importance of big data and artificial intelligence (AI) has led to an unprecedented shift in moving local computation into the cloud. One of the key drivers behind this transformation was the exploding cost of owning and maintaining large computing systems powerful enough to process these new workloads. Customers experience a reduced cost by renting only the required resources and only when needed, while data center operators benefit from efficiency at scale. A key factor in operating a profitable data center is a high overall utilization of its resources. Due to the scale of modern data centers, small improvements in efficiency translate to significant savings in the total cost of ownership (TCO). There are many important elements that constitute an efficient data center such as its location, architecture, cooling system, or the employed hardware. In this thesis, we focus on software-related aspects, namely the utilization of computational and memory resources. Reports from data centers operated by Alibaba and Google show that the overall resource utilization has stagnated at a level of around 50 to 60 percent over the past decade. This low average utilization is mostly attributable to peak demand-driven resource allocation despite the high variability of modern workloads in their resource usage. In other words, data centers today lack an efficient way to put idle resources that are reserved but not used to work. In this dissertation we present RackMem, a software-based solution to address the problem of low resource utilization through two main contributions. First, we introduce a disaggregated memory system tailored for virtual environments. We observe that virtual machines can use remote memory without noticeable performance degradation under moderate memory pressure on modern networking infrastructure. We implement a specialized remote paging system for QEMU/KVM that reduces the remote paging tail-latency by 98.2% in comparison to the state of the art. A job processing simulation at rack-scale shows that the total makespan can be reduced by 40.9% under our memory system. While seamless disaggregated memory helps to balance memory usage across nodes, individual nodes can still suffer overloaded resources if co-located workloads exhibit high resource usage at the same time. In a second contribution, we present a novel live migration technique for machines running on top of our remote paging system. Under this instant live migration technique, entire virtual machines can be migrated in as little as 100 milliseconds. An evaluation with in-memory key-value database workloads shows that the presented migration technique improves the state of the art by a wide margin in all key performance metrics. The presented software-based solutions lay the technical foundations that allow data center operators to significantly improve the utilization of their computational and memory resources. As future work, we propose new job schedulers and load balancers to make full use of these new technical foundations.Chapter 1. Introduction 1 1.1 Contributions of the Dissertation 3 Chapter 2. Background 5 2.1 Resource Disaggregation 5 2.2 Transparent Remote Paging 7 2.3 Remote Direct Memory Access (RDMA) 9 2.4 Live Migration of Virtual Machines 10 Chapter 3. RackMem Overview 13 3.1 RackMem Virtual Memory 13 3.2 RackMem Distributed Virtual Storage 14 3.3 RackMem Networking 15 3.4 Instant VM Live Migration 16 Chapter 4. Virtual Memory 17 4.1 Design Considerations for Achieving Low-latency 19 4.2 Pagefault handling 20 4.2.1 Fast-path and slow-path in the pagefault handler 21 4.2.2 State transition of RackVM page 23 4.3 Latency Hiding Techniques 25 4.4 Implementation 26 4.4.1 RackMem Virtual Memory Module 27 4.4.2 Dynamic Rebalancing of Local Memory 29 4.4.3 RackVM for Virtual Machines 29 4.4.4 Running Unmodified Applications 30 Chapter 5. RackMem Distributed Virtual Storage 31 5.1 The distributed Storage Abstraction 32 5.2 Memory Management 33 5.2.1 Remote memory allocation 33 5.2.2 Remote memory reclamation 33 5.3 Fault Tolerance 34 5.3.1 Fault-tolerance and Write-duplication 34 5.4 Multiple Storage Support in RackMem 36 5.5 Implementation 38 5.5.1 The Remote Memory Backend 38 5.5.2 Linux Demand Paging on RackDVS 39 Chapter 6. Networking 40 6.1 Design of RackNet 40 6.2 Implementation 41 6.2.1 RPC message layout 41 6.2.2 RackNet RPC Implementation 42 Chapter 7. Instant VM Live Migration 44 7.1 Motivation 45 7.1.1 The need for a tailored live migration technique 45 7.1.2 Software Bottlenecks 46 7.1.3 Utilizing workload variability 46 7.2 Design of Instant 47 7.2.1 Instant Region Migration 47 7.3 Implementation 48 7.3.1 Extension of RackVM for Instant 49 7.3.2 Instant region migration 49 7.3.3 Pre-fetch optimizations 51 7.3.4 Downtime optimizations 51 7.3.5 QEMU modification for Instant 52 Chapter 8. Evaluation - RackMem 53 8.1 Execution Environment 54 8.2 Pagefault Handler Latency 56 8.3 Single Application Performance 57 8.3.1 Batch-oriented Applications 58 8.3.2 Internal Pagesize and Performance 59 8.3.3 Write-duplication overhead 60 8.3.4 RackDVS slab size and performance 62 8.3.5 Latency-oriented Applications 63 8.3.6 Network Bandwidth Analysis 64 8.3.7 Dynamic Local Memory Partitioning 66 8.3.8 Rack-scale Job Processing Simulation 67 Chapter 9. Evaluation - Instant VM Live Migration 69 9.1 Experimental setup 69 9.2 Target Applications 70 9.3 Comparison targets 70 9.4 Database and client setups 71 9.5 Memory disaggregation scenarios 71 9.6.1 Time-to-responsiveness 71 9.6.2 Effective Downtime 73 9.6.3 Effect of Instant optimizations 75 Chapter 10. Conclusion 77 10.1 Future Directions 78 요약 89박