MorphoSys: efficient colocation of QoS-constrained workloads in the cloud

In hosting environments such as IaaS clouds, desirable application performance is usually guaranteed through the use of Service Level Agreements (SLAs), which specify minimal fractions of resource capacities that must be allocated for unencumbered use for proper operation. Arbitrary colocation of applications with different SLAs on a single host may result in inefficient utilization of the host’s resources. In this paper, we propose that periodic resource allocation and consumption models -- often used to characterize real-time workloads -- be used for a more granular expression of SLAs. Our proposed SLA model has the salient feature that it exposes flexibilities that enable the infrastructure provider to safely transform SLAs from one form to another for the purpose of achieving more efficient colocation. Towards that goal, we present MORPHOSYS: a framework for a service that allows the manipulation of SLAs to enable efficient colocation of arbitrary workloads in a dynamic setting. We present results from extensive trace-driven simulations of colocated Video-on-Demand servers in a cloud setting. These results show that potentially-significant reduction in wasted resources (by as much as 60%) are possible using MORPHOSYS.National Science Foundation (0720604, 0735974, 0820138, 0952145, 1012798

An Introduction to Control and Scheduling Co-Design

The paper presents the emerging field of integrated control and CPU-time scheduling, where more general scheduling models and methods that better suit the needs of control systems are developed. This creates possibilities for dynamic and flexible integrated control and scheduling frameworks, where the control design methodology takes the availability of computing resources into account during design and allows on-line trade-offs between control performance and computing resource utilization

Rate Monotonic vs. EDF: Judgment Day

Since the first results published in 1973 by Liu and Layland on the Rate Monotonic (RM) and Earliest Deadline First (EDF) algorithms, a lot of progress has been made in the schedulability analysis of periodic task sets. Unfortunately, many misconceptions still exist about the properties of these two scheduling methods, which usually tend to favor RMmore than EDF. Typical wrong statements often heard in technical conferences and even in research papers claim that RM is easier to analyze than EDF, it introduces less runtime overhead, it is more predictable in overload conditions, and causes less jitter in task execution. Since the above statements are either wrong, or not precise, it is time to clarify these issues in a systematic fashion, because the use of EDF allows a better exploitation of the available resources and significantly improves system’s performance. This paper comparesRMagainstEDFunder several aspects, using existing theoretical results, specific simulation experiments, or simple counterexamples to show that many common beliefs are either false or only restricted to specific situations

Towards Overhead-Free Interface Theory for Compositional Hierarchical Real-Time Systems

Much recent research has been conducted on compositional real-time scheduling framework as the framework becomes a useful fundamental theory for real-time OS-Hypervisor. Much recent research has been conducted on compositional real-time scheduling as the framework becomes a useful fundamental theory for real-time OS-Hypervisor. However, compositional frameworks suffer from abstraction overheads in composing components. In this paper, we classify the composition overheads into i) supply abstraction overhead associated with the supply from a resource provider, and ii) demand abstraction overhead associated with the component workload. Then, we provide sufficient conditions for each abstraction overhead to be eliminated. In addition, this paper provides a heuristic technique that transforms any component to satisfy the sufficient conditions so that the abstraction overheads are minimized. In our comparison, we showed our technique outperforms the prior overhead-reducing CF about 10% at average and other combination techniques about 8% in reducing the overhead

Scheduling Self-Suspending Tasks: New and Old Results

In computing systems, a job may suspend itself (before it finishes its execution) when it has to wait for certain results from other (usually external) activities. For real-time systems, such self-suspension behavior has been shown to induce performance degradation. Hence, the researchers in the real-time systems community have devoted themselves to the design and analysis of scheduling algorithms that can alleviate the performance penalty due to self-suspension behavior. As self-suspension and delegation of parts of a job to non-bottleneck resources is pretty natural in many applications, researchers in the operations research (OR) community have also explored scheduling algorithms for systems with such suspension behavior, called the master-slave problem in the OR community. This paper first reviews the results for the master-slave problem in the OR literature and explains their impact on several long-standing problems for scheduling self-suspending real-time tasks. For frame-based periodic real-time tasks, in which the periods of all tasks are identical and all jobs related to one frame are released synchronously, we explore different approximation metrics with respect to resource augmentation factors under different scenarios for both uniprocessor and multiprocessor systems, and demonstrate that different approximation metrics can create different levels of difficulty for the approximation. Our experimental results show that such more carefully designed schedules can significantly outperform the state-of-the-art

On the Optimality of RM and EDF for Non-Preemptive Real-Time Harmonic Tasks

ABSTRACT In this paper, we study non-preemptive uniprocessor realtime scheduling using the non-preemptive RM (npRM) and EDF (npEDF) scheduling algorithms. We discuss the limitations of existing studies, identifying pessimism in current schedulability analysis and inefficiencies in existing processor speedup results. Focusing on harmonic task sets, we show that even with restrictions placed on the execution times of the tasks, npRM and npEDF are not able to schedule all feasible task sets. We obtain necessary conditions for the feasibility of the harmonic tasks with arbitrary integer period ratios. Then we derive sufficient conditions for the schedulability of npRM and npEDF upon harmonic task sets. Based on these conditions, a superior speedup factor which guarantees the schedulability in cases where there are fewer restrictions on the execution times is derived. Results from simulation experiments show an average speedup factor three times less than the only existing feasible method to obtain speedup factor

Converting existing analysis to the EDP resource model

In (hard) real-time embedded systems, it is necessary to guarantee that tasks always meet their deadlines i.e. results should neither be too early nor too late. In the context of fixed-priority systems, this is usually done by performing schedulability analysis in which the (best-case and) worst-case response-time of each task is computed and compared with its (best-case) worst-case deadline to determine schedulability. Resource reservation has been proposed as a means to provide temporal isolation between applications. Building upon this notion, hierarchical scheduling frameworks for different resource models have been proffered in the literature with complementary schedulability conditions. Unfortunately, these novel ideas do not directly allow for the reuse of existing results, but rather favor derivations from first principles. In this document, we investigate a means to reuse existing results from non-hierarchical scheduling theory by modeling the unavailability of a resource in a two-level hierarchical framework using two fictive tasks with highest priorities. We show that this novel method using our unavailability model not only allows for unifying the analysis but can also be easily applied in determining linear response-time upper bounds. For the latter, we also consider approaches for obtaining tighter bounds for harmonic tasks