Browsing by Subject "Markov modeling"

Now showing 1 - 4 of 4

Open Access
Analysis of concurrency control protocols for real-time database systems
(Elsevier, 1998) Ulusoy, Özgür
This paper provides an approximate analytic solution method for evaluating the performance of concurrency control protocols developed for real-time database systems (RTDBSs). Transactions processed in a RTDBS are associated with timing constraints typically in the form of deadlines. The primary consideration in developing a RTDBS concurrency control protocol is the fact that satisfaction of the timing constraints of transactions is as important as maintaining the consistency of the underlying database. The proposed solution method provides the evaluation of the performance of concurrency control protocols in terms of the satisfaction rate of timing constraints. As a case study, a RTDBS concurrency control protocol, called High Priority, is analyzed using the proposed method. The accuracy of the performance results obtained is ascertained via simulation. The solution method is also used to investigate the real-time performance benefits of the High Priority over the ordinary Two-Phase Locking.
Open Access
Analysis of design parameters in safety-critical computers
(IEEE Computer Society, 2018) Ahangari, H.; Atik, F.; Ozkok, Y. I.; Yildirim, A.; Ata, S. O.; Ozturk, O.
Nowadays, safety-critical computers are extensively used in many civil domains like transportation including railways, avionics, and automotive. In evaluating these safety critical systems, previous studies considered different metrics, but some of safety design parameters like failure diagnostic coverage (C) or common cause failure (CCF) ratio have not been seriously taken into account. Moreover, in some cases safety has not been compared with standard safety integrity levels (IEC-61508: SIL1-SIL4) or even have not met them. Most often, it is not very clear that which part of the system is the Achilles heel and how design can be improved to reach standard safety levels. Motivated by such design ambiguities, we aim to study the effect of various design parameters on safety in some prevalent safety configurations, namely, 1oo2 and 2oo3, where 1oo1 is also used as a reference. By employing Markov modeling, we analyzed the sensitivity of safety to important parameters including: failure rate of processor, failure diagnostic coverage, CCF ratio, test and repair rates. This study aims to provide a deeper understanding on the influence of variation in design parameters over safety. Consequently, to meet appropriate safety integrity level, instead of improving some parts of a system blindly, it will be possible to make an informed decision on more relevant parameters. IEEE
Open Access
Analysis of design parameters in SIL-4 safety-critical computer
(IEEE, 2017-01) Ahangari, Hamzeh; Özkök, Y. I.; Yıldırım, A.; Say, F.; Atik, Funda; Öztürk, Özcan
Nowadays, Safety-critical computers are extensively used in may civil domains like transportation including railways, avionics and automotive. We noticed that in design of some previous works, some critical safety design parameters like failure diagnostic coverage (DC) or common cause failure (CCF) ratio have not been seriously taken into account. Moreover, in some cases safety has not been compared with standard safety levels (IEC-61508 SIL1-SIL4) or even have not met them. Most often, it is not very clear that which part of the system is the Achilles' heel and how design can be improved to reach standard safety levels. Motivated by such design ambiguities, we aim to study the effect of various design parameters on safety in some prevalent safety configurations: 1oo2 and 2oo3. 1oo1 is also used as a reference. By employing Markov modeling, sensitivity of safety to each of the following critical design parameters is analyzed: failure rate of processing element, failure diagnostics coverage, common cause failures and repair rates. This study gives a deeper sense regarding influence of variation in design parameters over safety. Consequently, to meet appropriate safety integrity level, instead of improving some system parts blindly, it will be possible to make an informed decision on more relevant parameters. © 2017 IEEE.
Open Access
Custom hardware optimizations for reliable and high performance computer architectures
(2020-09) Ahangari, Hamzeh
In recent years, we have witnessed a huge wave of innovations, such as in Artificial Intelligence (AI) and Internet-of-Things (IoT). In this trend, software tools are constantly and increasingly demanding more processing power, which can no longer be met by processors traditionally. In response to this need, a diverse range of hardware, including GPUs, FPGAs, and AI accelerators, are coming to the market every day. On the other hand, while hardware platforms are becoming more power-hungry due to higher performance demand, concurrent reduction in the size of transistors, and placing high emphasis on reducing the voltage, altogether have always been sources of reliability concerns in circuits. This particularly is applicable to error-sensitive applications, such as transportation and aviation industries where an error can be catastrophic. The reliability issues may have other reasons too, like harsh environmental conditions. These two problems of modern electronic circuits, meaning the need for higher performance and reliability at the same time, require appropriate solutions. In order to satisfy both the performance and the reliability constraints either designs based on reconfigurable circuits, such as FPGAs, or designs based on Commercial-Off-The-Shelf (COTS) components like general-purpose processors, can be an appropriate approach because the platforms can be used in a wide variety of applications. In this regard, three solutions have been proposed in this thesis. These solutions target 1) safety and reliability at the system-level using redundant processors, 2) performance at the architecture-level using multiple accelerators, and 3) reliability at the circuit-level through the use of redundant transistors. Specifically, in the first work, the contribution of some prevalent parameters in the design of safetycritical computers, using COTS processors, is discussed. Redundant architectures are modeled by the Markov chains, and sensitivity of system safety to parameters has been analyzed. Most importantly, the significant presence of Common Cause Failures (CCFs) has been investigated. In the second work, the design, and implementation of an HLS-based, FPGA-accelerated, high-throughput/work-efficient, synthesizable template-based graph processing framework has been presented. The template framework is simplified for easy mapping to FPGA, even for software programmers. The framework is particularly experimented on Intel state-ofthe-art Xeon+FPGA platform to implement iterative graph algorithms. Beside high-throughput pipeline, work-efficient mode significantly reduces total graph processing run-time with a novel active-list design. In the third work, Joint SRAM (JSRAM) cell, a novel circuit-level technique to exploit the trade-off between reliability and memory size, is introduced. This idea is applicable to any SRAM structure like cache memory, register file, FPGA block RAM, or FPGA look-up table (LUT), and even latches and Flip-Flops. In fault-prone conditions, the structure can be configured in such a way that four cells are combined together at the circuit level to form one large and robust memory bit. Unlike prevalent hardware redundancy techniques, like Triple Modular Redundancy (TMR), there is no explicit majority voter at the output. The proposed solution mainly focuses on transient faults, where the reliable mode can provide auto-correction and full immunity against single faults.