In object-oriented programming, updates to the state variables of objects (by the methods of the object) have to be protected through semaphores to ensure mutual exclusion. Semaphore operations are invoked each time a...
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ISBN:
(纸本)0818680164
In object-oriented programming, updates to the state variables of objects (by the methods of the object) have to be protected through semaphores to ensure mutual exclusion. Semaphore operations are invoked each time an, object is accessed, and this represents significant run-time overhead. This a's of special concern in cost-conscious, small-size embedded systems such as those used in automotive applications - where costs must be kept to an absolute minimum. Object-oriented programming can be feasible an such applications only if the OS provides efficient, lour-overhead semaphores. We present a new semaphore implementation scheme which saves one context switch per semaphore lod operation in most circumstances and gives performance improvements of 18-25% over traditional semaphore implementation schemes.
We propose a model for quality-of-service (QoS) negotiation in building real-time services to meet both predictability and graceful degradation requirements. QoS negotiation is shown to (i) outperform conventional ...
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ISBN:
(纸本)0818680164
We propose a model for quality-of-service (QoS) negotiation in building real-time services to meet both predictability and graceful degradation requirements. QoS negotiation is shown to (i) outperform conventional ''binary'' admission control schemes (either guaranteeing the required QoS or rejecting the service request), and (ii) achieve higher application-perceived system utility. We incorporated the proposed QoS-negotiation model into an example realtime middleware service, called RTPOOL, which manages a distributed pool of shared computing resources (processors) to guarantee timeliness QoS for real-time applications. The efficacy and power of QoS negotiation are demonstrated for an automated flight control system implemented on a network of PCs running RTPOOL. This system is used to fly an F-16 fighter aircraft modeled using the Aerial Combat (ACM) F-16 Flight Simulator. Experimental results indicate that QoS negotiation, while maintaining real-time guarantees, enables graceful QoS degradation under conditions in which traditional schedulability analysis and admission control schemes fail.
In Shepard and Gagne [1], a branch-and-bound implicit enumeration algorithm is described whose purpose is to generate a feasible schedule, if any, for each processor on a multiprocessing node running hard real-time pr...
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An effective failure-detection scheme is essential for reliable communication services. Most computer network rely on behavior-based detection schemes: each node uses heartbeats to detect the failure of its neighbor n...
For many applications it is important to provide communication services with guaranteed timeliness and fault-tolerance at an acceptable level of overhead. In this paper, we present a scheme for restoring real-time cha...
ISBN:
(纸本)9780897919050
For many applications it is important to provide communication services with guaranteed timeliness and fault-tolerance at an acceptable level of overhead. In this paper, we present a scheme for restoring real-time channels, each with guaranteed timeliness, from component failures in multi-hop networks. To ensure fast/guaranteed recovery, backup channels are set up a priori in addition to each primary channel. That is, a dependable real-time connection consists of a primary channel and one or more backup channels. If a primary channel fails, one of its backup channels is activated to become a new primary channel. We describe a protocol which provides an integrated solution to the failure-recovery problem (i.e., channel switching, resource re-allocation, ...). We also present a resource sharing method that significantly reduces the overhead of backup channels. The simulation results show that good coverage (in recovering from failures) can be achieved with about 30% degradation in network utilization under a reasonable failure condition. Moreover, the fault-tolerance level of each dependable connection can be controlled, independently of other connections, to reflect its criticality.
This paper examines the problem of schedule revision in a distributed job shop where the object is to minimize the global makespan. Schedules of work cells may interact through precedence constraints, and a work cell&...
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This paper examines the problem of schedule revision in a distributed job shop where the object is to minimize the global makespan. Schedules of work cells may interact through precedence constraints, and a work cell's response to a local schedule disruption may affect schedules of other cells. Complete knowledge about how local schedule changes affect the global schedule may require global knowledge about the schedule. Here, we show that knowledge of only local constraints may be almost as useful as global knowledge for the revision of one cell's schedule. We present simulation results from a general distributed job shop model.
In object-oriented programming, updates to the state variables of objects (by the methods of the object) have to be protected through semaphores to ensure mutual exclusion. Semaphore operations are invoked each time a...
详细信息
In object-oriented programming, updates to the state variables of objects (by the methods of the object) have to be protected through semaphores to ensure mutual exclusion. Semaphore operations are invoked each time an object is accessed, and this represents significant run-time overhead. This is of special concern in cost-conscious, small-size embedded systems-such as those used in automotive applications-where costs must be kept to an absolute minimum. Object-oriented programming can be feasible in such applications only if the OS provides efficient, low-overhead semaphores. The authors present a new semaphore implementation scheme which saves one context switch per semaphore lock operation in most circumstances and gives performance improvements of 18-25% over traditional semaphore implementation schemes.
An effective failure-detection scheme is essential for reliable communication services. Most computer network rely on behavior-based detection schemes: each node uses heartbeats to detect the failure of its neighbor n...
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An effective failure-detection scheme is essential for reliable communication services. Most computer network rely on behavior-based detection schemes: each node uses heartbeats to detect the failure of its neighbor nodes, and the transport protocol (like TCP) achieves reliable communication by acknowledgment/retransmission. In this paper, we experimentally evaluate the effectiveness of such behavior-based detection schemes in real-time communication. Specifically, we measure and analyze the coverage and latency of two failure-detection schemes-neighbor detection and end-to-end detection-through fault-injection experiments. The experimental results have shown that a significant portion of failures can be detected very quickly by the neighbor detection scheme, while the end-to-end detection scheme uncovers the remaining failures with larger detection latencies.
Since real-time applications usually require not only timeliness but also fault-tolerance, it is essential to incorporate fault-tolerance into real-time communication services that are indispensable to distributed rea...
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Since real-time applications usually require not only timeliness but also fault-tolerance, it is essential to incorporate fault-tolerance into real-time communication services that are indispensable to distributed real-time applications. The techniques for failure recovery in datagram communication are not adequate for real-time communication, because they cannot provide recovery-delay guarantees. To ensure fast recovery of a real-time channel from network component failures, we need to reserve network resources (spare resources) along a backup route before failures actually occur. The focus of this paper is on minimizing the amount of spare resources while meeting the fault-tolerance requirement. Specifically, we present resource sharing mechanisms and backup-route selection algorithms, and evaluate their efficiency with extensive simulations.
We propose a model for quality-of-service (QoS) negotiation in building real-time services to meet both predictability and graceful degradation requirements. QoS negotiation is shown to (i) outperform conventional &qu...
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We propose a model for quality-of-service (QoS) negotiation in building real-time services to meet both predictability and graceful degradation requirements. QoS negotiation is shown to (i) outperform conventional "binary" admission control schemes (either guaranteeing the required QoS or rejecting the service request), and (ii) achieve higher application-perceived system utility. We incorporated the proposed QoS-negotiation model into an example real-time middleware service, called RTPOOL, which manages a distributed pool of shared computing resources (processors) to guarantee timeliness QoS for real-time applications. The efficacy and power of QoS negotiation are demonstrated for an automated flight control system implemented on a network of PCs running RT-POOL. This system is used to fly an F-16 fighter aircraft modeled using the Aerial Combat (ACM) F-16 Flight Simulator. Experimental results indicate that QoS negotiation, while maintaining real-time guarantees, enables graceful QoS degradation under conditions in which traditional schedulability analysis and admission control schemes fail.
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