Conference Paper

Tradeoff Exploration between Reliability, Power Consumption, and Execution Time.

DOI: 10.1007/s10009-012-0263-9 Conference: Computer Safety, Reliability, and Security - 30th International Conference, SAFECOMP 2011, Naples, Italy, September 19-22, 2011. Proceedings
Source: DBLP

ABSTRACT For autonomous critical real-time embedded (e.g., satellite), guaranteeing a very high level of reliability is as important as keeping the power consumption as low as possible. We propose an off-line scheduling heuristic which, from a given software application graph and a given multiprocessor architecture (homogeneous and fully connected), produces a static multiprocessor schedule that optimizes three criteria: its length (crucial for real-time systems), its reliability (crucial for dependable systems), and its power consumption (crucial for autonomous systems). Our tricriteria scheduling heuristic, called TSH, uses the active replication of the operations and the data-dependencies to increase the reliability and uses dynamic voltage and frequency scaling to lower the power consumption. We demonstrate the soundness of TSH. We also provide extensive simulation results to show how TSH behaves in practice: first, we run TSH on a single instance to provide the whole Pareto front in 3D; second, we compare TSH versus the ECS heuristic (Energy-Conscious Scheduling) from the literature; and third, we compare TSH versus an optimal Mixed Linear Integer Program.

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    • "Because the failure rate˜λ 0 is usually very small, of the order of 10 −5 per time unit [2], or even 10 −6 [7] [16], we can use the first order approximation of R i (f ) as "
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    ABSTRACT: In this paper, we consider the problem of scheduling an application on a parallel computational platform. The application is a particular task graph, either a linear chain of tasks, or a set of independent tasks. The platform is made of identical processors, whose speed can be dynamically modified. It is also subject to failures: if a processor is slowed down to decrease the energy consumption, it has a higher chance to fail. Therefore, the scheduling problem requires to re-execute or replicate tasks (i.e., execute twice a same task, either on the same processor, or on two distinct processors), in order to increase the reliability. It is a tri-criteria problem: the goal is to minimize the energy consumption, while enforcing a bound on the total execution time (the makespan), and a constraint on the reliability of each task. Our main contribution is to propose approximation algorithms for these particular classes of task graphs. For linear chains, we design a fully polynomial time approximation scheme. However, we show that there exists no constant factor approximation algorithm for independent tasks, unless P=NP, and we are able in this case to propose an approximation algorithm with a relaxation on the makespan constraint.
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    • "• Re-execution: it consists in re-executing a task that does not meet the reliability constraint, see [14]. • Replication: this model, studied in [1], consists in executing the same task on p different processors simultaneously , in order to meet the reliability constraints. • Checkpointing: this model, studied in [11], consists in " saving " the work done at some certain points of the work, hence reducing the amount of work lost when a failure occurs. "
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    ABSTRACT: This paper presents several energy-aware scheduling algorithms whose design is optimized for different speed models. Dynamic Voltage and Frequency Scaling (DVFS) is a model frequently used to reduce the energy consumption of a schedule, but it has negative effect on reliability. While the reliability of a schedule can sometimes be neglected (battery powered systems such as cell-phones or personal computers), it becomes extremely important when considering massively parallel architectures (petascale, exascale). In this work, we consider the problem of minimizing the energy within a makespan constraint. Additionally, we consider two models, one that takes into account a reliability constraint, and one that does not. We assume that the mapping is given, say by an ordered list of tasks to execute on each processor, and we aim at optimizing the energy consumption while enforcing a prescribed bound on the execution time. While it is not possible to change the allocation of a task, it is possible to change its speed. Rather than using a local approach such as backfilling, we consider the problem as a whole and study the impact of several speed variation models on its complexity. To improve the reliability of a schedule while reducing the energy consumption, we allow for the re-execution of some tasks. We present several results in that framework, as well as future research plans.
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    • "Because the fault rate is usually very small, of the order of 10 −6 per time unit in [5] [16], 10 −5 in [1], we can use the first order approximation of R i (f i ) as "
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    ABSTRACT: We consider a task graph mapped on a set of homogeneous processors. We aim at minimizing the energy consumption while enforcing two constraints: a prescribed bound on the execution time (or makespan), and a reliability threshold. Dynamic voltage and frequency scaling (DVFS) is an approach frequently used to reduce the energy consumption of a schedule, but slowing down the execution of a task to save energy is decreasing the reliability of the execution. In this work, to improve the reliability of a schedule while reducing the energy consumption, we allow for the re-execution of some tasks. We assess the complexity of the tri-criteria scheduling problem (makespan, reliability, energy) of deciding which task to re-execute, and at which speed each execution of a task should be done, with two different speed models: either processors can have arbitrary speeds (continuous model), or a processor can run at a finite number of different speeds and change its speed during a computation (VDD model). We propose several novel tri-criteria scheduling heuristics under the continuous speed model, and we evaluate them through a set of simulations. The two best heuristics turn out to be very efficient and complementary.
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