| 1. |
- Leva, Alberto, et al.
(author)
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A general control-theoretical methodology for runtime resource allocation in computing systems
- 2013
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In: 2013 IEEE 52nd Annual Conference on Decision and Control, CDC 2013. - 0191-2216. - 9781467357173 ; , s. 3487-3492
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Conference paper (peer-reviewed)abstract
- Control theory is emerging as a source of solutions for many problems in the computing systems domain, and in particular for resource allocation. However, the techniques proposed to date in the literature, do not successfully address the difficulty of devising allocation schemes that are general enough, provide stability guarantees, and can be parametrised and managed by system administrators, or computing systems' practitioners at large. This paper proposes a two-level timevarying control scheme for the allocation of a generic resource, and proves its stability. In addition, the paper discusses how the scheme can be made acceptable by computing systems administrators, and how to tune the involved parameters. A simulation campaign is reported, validating the aforementioned claims.
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| 2. |
- Leva, Alberto, et al.
(author)
-
Control-Based Operating System Design
- 2013
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Book (other academic/artistic)abstract
- Control-Based Operating System Design describes the application of system- and control-theoretical methods to the design of computer operating system components. It argues that computer operating system components should not be first “designed" and then “endowed with control", but rather conceived from the outset as controllers, synthesised and assessed in the system-theoretical world of dynamic models, and then realised as control algorithms. Doing so is certainly a significant perspective shift with respect to current practices in operating system design, but the payoff is significant too. In some sense, adopting the suggested attitude means viewing computing systems as cyber-physical ones, where the operating system plays the computational role, the physical elements are the managed resources, and the various (control) functionalities to be realised, interact and co-operate as a network. The book includes both a theoretical treatment of the usefulness of the approach, and the description of a complete implementation in the form of a microcontroller kernel, made available as free software. Topics covered include modelling and control design paradigms, task scheduling, resource allocation, application performance control, sensing and actuating, and the implementation and assessment of Miosix, a control-based kernel.
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| 3. |
- Leva, Alberto, et al.
(author)
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Disturbance rejection in autotuners: an assessment method and a rule proposal
- 2015
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In: American Control Conference (ACC), 2015. - 9781479986842 ; , s. 2876-2881
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Conference paper (peer-reviewed)abstract
- Disturbance rejection is a primary objective in many industrial control loops, thus a relevant goal for autotuning controllers. Nonetheless, autotuning has invariantly to cope with a reduced amount of process information. As a consequence, with the standard single-loop structure typically adopted in the addressed context, effective disturbance rejection calls for strong feedback, and therefore the solutions available to date fall sometimes short of perfection. This paper discusses the matter basically from a methodological standpoint, evidencing some structural reasons for the observed shortcomings. The result is a synthesis approach improving rejection performance with respect to existing and well established tuning rules, on a rigorously sound basis. Simulation examples are presented to support the proposal.
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| 4. |
- Leva, Alberto, et al.
(author)
-
Explicit Model-Based Real PID Tuning for Efficient Load Disturbance Rejection
- 2019
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In: Industrial & Engineering Chemistry Research. - : AMER CHEMICAL SOC. - 0888-5885 .- 1520-5045. ; 58:51, s. 23211-23224
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Journal article (peer-reviewed)abstract
- In the process control, many PID loops are primarily devoted to rejecting load disturbances, and some of them are crucial for the quality of the overall plant operation. In such a scenario, automatic tuning is highly desired. However, load disturbance rejection calls for strong feedback up to quite high frequencies with respect to the dominant plant dynamics, on which most tuning rules are centered. As such it is difficult for a rule to yield good and, above all, uniform results in the face of all the various process structures it can be confronted with. In this paper, we propose an explicit model-based PID tuning rule specifically targeted at the problem just evidenced. The rule minimizes the magnitude of the nominal disturbance-to-output frequency response, at the same time preventing that magnitude to exhibit a peak or a plateau around its maximum. This characteristic, together with tuning the PID derivative filter, leads to sharp disturbance rejection without incurring in an excessive control sensitivity to high-frequency measurement noise and mitigates the problems caused by heterogeneous process dynamics. The proposed approach is assessed by comparing the rule with selected counterparts, on a literature benchmark with different process structures. A laboratory experiment is finally presented to show that our rule can withstand real-world operating conditions.
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| 5. |
- Leva, Alberto, et al.
(author)
-
High-Precision Low-Power Wireless Nodes' Synchronization via Decentralized Control
- 2016
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In: IEEE Transactions on Control Systems Technology. - United States : IEEE. - 1063-6536 .- 1558-0865. ; 24:4, s. 1279-1293
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Journal article (peer-reviewed)abstract
- Abstract: Time synchronization is crucial for wireless sensor networks (WSNs), where operations often rely on time ordering of events. WSNs are deployed in different scenarios, and therefore their timing requirements are often related to the peculiar characteristics of the specific environment they have to act in. Synchronization is anyway always an issue: transactional applications need monotonicity of the nodes' clocks to avoid time reversal, ultralow power applications call for minimal overhead to allow for low-duty-cycle operation, applications facing extreme environments have to maintain the needed precision in the presence of unforeseen thermal drift, and so on. Specially, control applications on battery-powered devices, where timing is an issue and low-power operation is highly desired, benefit from synchronization. However, to date, the problem of synchronization has been differently faced depending on the application domain. This paper proposes a general solution to the problem of synchronization in WSNs, which seamlessly integrates with the radio stack. In addition, it guarantees monotonic and continuous node clocks with low overhead for the infrastructure. The solution is based on a decentralized control scheme that is stable and robust to thermal stress, without the need for temperature measurements. The control scheme is simulated and implemented on real WSN nodes. The efficiency of the scheme is evaluated with simulations and experiments, providing insights on the maximum synchronization error between nodes, on the communication overhead, and on the limited nodes' power consumption. The solution is also compared with state-of-the-art alternatives.
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| 6. |
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| 7. |
- Leva, Alberto, et al.
(author)
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How control-friendly is a computing system? And how control-friendly could it be?
- 2020
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In: 21th IFAC World Congress. - : Elsevier BV. - 2405-8963. ; 53, s. 7857-7864
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Conference paper (peer-reviewed)abstract
- To date, not that much. Improvements are possible, but some system-theoretically grounded re-design is necessary. We discuss the matter based on our experience, and as a consequence, we come to distilling some design clues and research directions.
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| 8. |
- Leva, Alberto, et al.
(author)
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Modelling and Control of Big Data Frameworks
- 2017
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In: IFAC-PapersOnLine, Vol. 50. - : Elsevier BV. ; , s. 6110-6115
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Conference paper (peer-reviewed)abstract
- We present a model library conceived to design and assess critical components of big data frameworks, with a control-centric approach. The library adopts the object-oriented paradigm, using the Modelica language. Continuous-time and algorithmic models can be mixed, allowing to represent control code with high fidelity, and to reduce the simulation effort to the minimum required. We discuss the used modelling principles, describe the library, and show some design examples.
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| 9. |
- Leva, Alberto, et al.
(author)
-
Object-Oriented Modelling and Simulation of Air Flow in Data Centres Based on a Quasi-3D Approach for Energy Optimisation
- 2014
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In: IEEE/ACM 7th International Conference on Utility and Cloud Computing (UCC), (6th Cloud Control Workshop). - 9781479978816 ; , s. 554-559
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Conference paper (peer-reviewed)abstract
- Cloud computing has recently received considerable attention, as a promising approach for delivering ICT services by improving the utilisation of data centre resources. On the other hand, the increased usage of ICT, jointly with the increased cost of energy, make designing and managing data centres with energy efficient strategies a crucial and strategical problem. In the literature there are many studies based on Computational Fluid Dynamics (CFD) simulation models. While the obtained results are usually very reliable and accurate, the massive use of such models for control design require a large amount of time due to their computational complexity and scarce flexibility. In addition, CFD models are usually quite sensitive to any kind of change to the operating conditions, e.g. when varying the considered load balancing algorithm. In this paper, we propose a modelling and simulation framework suited for control design, that is able to simulate both heating and energy phenomena, and different load balancing strategies in a data centre. The purpose of this work is to provide a tool to perform energy-efficiency targeted studies, providing accurate and reliable results.
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| 10. |
- Leva, Alberto, et al.
(author)
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Progress Rate Control for Computer Applications
- 2018
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In: 17th annual European Control Conference ECC18. - Limassol, Cyprus. - 9783952426982 ; , s. 3173-3178
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Conference paper (peer-reviewed)abstract
- Self-adaptive software applications often include some form of progress rate control. Various frameworks were proposed to measure progress and provision resources to govern it, hence - in control terms - for sensors and actuators. The same is not true for control laws, however. In this paper we address this part of the overall problem, proposing a standard control structure that can be easily configured and tuned to match a variety of progress control needs. We completely analyse the simplest case, namely a single application under fixed rate control, and spend a few words on extensions to multiple application and event-based realisation. Simulation examples are reported to support the proposal.
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