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- Voigt, Thiemo
(författare)
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Architectures for Service Differentiation in Overloaded Internet Servers
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Web servers become overloaded when one or several server resources such as network interface, CPU and disk become overutilized. Server overload leads to low server throughput and long response times experienced by the clients. Traditional server design includes only marginal or no support for overload protection. This thesis presents the design, implementation and evaluation of architectures that provide overload protection and service differentiation in web servers. During server overload not all requests can be processed in a timely manner. Therefore, it is desirable to perform service differentiation, i.e., to service requests that are regarded as more important than others. Since requests that are eventually discarded also consume resources, admission control should be performed as early as possible in the lifetime of a web transaction. Depending on the workload, some server resources can be overutilized while the demand on other resources is low because certain types of requests utilize one resource more than others. The implementation of admission control in the kernel of the operating system shows that this approach is more efficient and scalable than implementing the same scheme in user space. We also present an admission control architecture that performs admission control based on the current server resource utilization combined with knowledge about resource consumption of requests. Experiments demonstrate more than 40% higher throughput during overload compared to a standard server and several magnitudes lower response times. This thesis also presents novel architectures and implementations of operating system support for predictable service guarantees. The Nemesis operating system provides applications with a guaranteed communication service using the developed TCP/IP implementation and the scheduling of server resources. SILK (Scout in the Linux kernel) is a new networking stack for the Linux operating system that is based on the Scout operating system. Experiments show that SILK enables prioritizing and other forms of service differentiation between network connections while running unmodified Linux applications.
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- Carlsson, Leif
(författare)
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Framväxten av en intern redovisning i Sverige. 1900-1945
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, the historical development of cost accounting in Sweden right up to 1945 is examined. The study has been divided into three periods, 1900-1918, 1919-1936 and 1937-1945 and an examination of the relevant literature, mainly contemporary, has been made. To obtain a notion of the situation prevailing in the companies of the time a number of papers written by students at the Stockholm School of Economics have been analysed. These students had visited various firms and written about their cost accounting systems.The study has been made with the main purpose of giving an account of how cost accounting has developed from a technical point of view. A systematic survey has been carried out using a working model built around elements of costs, cost centres and cost objectives. Another purpose has been to examine the factors which could have influenced the design of cost accounting systems during the period. Therefore, a review of the earlier development in Sweden, the Anglo-Saxon countries and Germany has proved to be important for understanding the rise of cost accounting in Sweden.The development of cost accounting is characterized by the standardization process which went on from 1927 to 1945. This thesis is based on three important standardization proposals, namely that of 1931 regarding terminology, that of 1936 regarding product calculation (full costing) and that of 1945 regarding a normal chart of accounts for industry. Therefore, a theory of standardization is the foundation for this thesis. Institutional theory is referred to as an explanation of how different factors influenced the design of the cost accounting system.There are important conclusions to be drawn. Looking at the cost accounting system certain tendencies can be distinguished: A change was made from after-calculation to pre-calculation; normal costing was recommended; full costing prevailed with a strong connection to accounting and there was a striving for the standardization of terminology, calculations and chart of accounts. The influence from Germany was an important driving force during the whole period. Certain individuals have exerted a strong influence on the design of cost accounting systems. The price changes during and after the First World War gave impulses to use current acquisition costs. Education in cost accounting has had an important influence on the development and an interplay between theory and practice has taken place, since the teachers in higher education also often worked in firms in those days. Naturally, standardization itself has played a dominant part in the development of cost accounting in Sweden.
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- Gustafsson, Jan
(författare)
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Analyzing execution-time of object-oriented programs using abstract interpretation
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- As a result of the industrial deployment of real-time systems, there is an increasing demandfor methods to perform safe and tight calculation of the worst case execution time (WCET) ofprograms. The WCET is a necessary prerequisite for guaranteeing correct timing behaviour ofreal-time systems. WCET calculation means to find the path, often among a huge number ofpaths, that takes the longest time to execute. The calculation is based on path information for theprogram, such as the maximum number of iterations in loops and identification of paths that arenever executed. In most existing WCET analysis methods, this information is given as manual annotations by the programmer. In this thesis we present a method which automatically calculates path information for object-oriented real-time programs by static analysis. Thus, the method can be used in automating the WCET analysis, thereby relieving the programmer from the tedious and error-prone manualannotation work. The method, which is based on abstract interpretation, generates safe but not necessarily exactpath information. A trade-off between quality and calculation cost has to be made, since findingthe exact information is a complex, often intractable problem for non-trivial programs. We show how the general abstract interpretation theory can be used, in a structured way, toapproximate the semantics of an imperative or object-oriented programming language. We have chosen to analyze RealTimeTalk (RTT), an object-oriented language based on Smalltalk,and have developed a prototype tool which implements our analysis for a subset of the language,We show that the tool is capable of analyzing programs with a complexity which would makemanual annotation of the program all but trivial.
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- Kindahl, Mats, 1967-
(författare)
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Verification of Infinite-State Systems : Decision Problems and Efficient Algorithms
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents methods for the verification of distributed systems with infinite state spaces. We consider several verification problems for lossy channel systems, a class of infinite-state systems consisting of finite-state machines that communicate over unbounded, but lossy, FIFO channels. We also combine partial order techniques with symbolic techniques to improve performance of verification algorithms for infinite state systems.We study several implementation relations between lossy channel systems and finite transition systems, and show decidability of the following problems: trace inclusion, trace equivalence, simulation preorder, bisimulation equivalence, weak bisimulation equivalence in both directions, and weak simulation preorder in one direction. We further show that weak simulation preorder in the other direction is undecidable.Partial order reduction techniques are utilised to avoid exploring multiple interleavings of independent transitions. Constraint systems are introduced as a symbolic technique to represent (possibly infinite) sets of states. We present general methods for the application of partial order techniques for the verification of constraint systems. The method described is used for checking safety properties using forward or backward reachability analysis. It is based on the use of a—not necessarily symmetric—commutativity relation between operations. In contrast with previously existing approaches to partial order verification, which are based on a symmetric relation on transitions, our method does not require the relation to be symmetric. Partial order verification methods for lossy channel systems and for unsafe (i.e., infinite-state) Petri nets are developed to demonstrate the applicability of this approach.
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