The goal of Denali is to safely execute many independent, untrusted server applications on a single physical machine. This would enable any developer to inject a new service into third-party Internet infrastructure; for example, dynamic content generation code could be introduced into content-delivery networks or caching systems. We believe that virtual machine monitors (VMMs) are ideally suited to this application domain. A VMM provides strong isolation by default, since one virtual machine cannot directly name a resource in another. In addition, VMMs defer the implementation of high-level abstractions to guest OSs, which greatly simplifies the kernel and avoids "layer-below" attacks. The main challenge in using a VMM for this application domain is in scaling the number of concurrent virtual machines that can simultaneously execute on it.

In this paper, we present surplus fair scheduling (SFS), a proportional-share CPU scheduler designed for symmetric multiprocessors. We first show that the infeasibility of certain weight assignments in multiprocessor environments results in unfairness or starvation in many existing proportional-share schedulers. We present a novel weight readjustment algorithm to translate infeasible weight assignments to a set of feasible weights. We show that weight readjustment enables existing proportional-share schedulers to significantly reduce, but not eliminate, the unfairness in their allocations. We then present surplus fair scheduling, a proportional-share scheduler that is designed explicitly for multiprocessor environments. We implement our scheduler in the Linux kernel and demonstrate its efficacy through an experimental evaluation. Our results show that SFS can achieve proportionate allocation, application isolation and good interactive performance, albeit at a slight increase in scheduling overhead. We conclude from our results that a proportionalshare scheduler such as SFS is not only practical but also desirable for server operating systems.

* The current World-Wide Web service model treats all requests equivalently, both while being processed by servers and while being transmitted over the network. For some uses, such as web prefetching or multiple priority schemes, different levels of service are desirable. This paper presents three simple, server-side, application -level mechanisms (limiting process pool size, lowering process priorities, limiting transmission rate) to provide two different levels of web service (regular and low priority). We evaluated the performance of these mechanisms under combinations of two foreground workloads (light and heavy) and two levels of available network bandwidth (10Mb/s and 100Mb/s). Our experiments show that even with background traffic sufficient to saturate the network, foreground performance is reduced by at most 4-17%. Thus, our user-level mechanisms can effectively provide different service classes even in the absence of operating system and network support. 1. Introduction The ...

In this paper, we present Deadline Fair Scheduling (DFS), a proportionate-fair CPU scheduling algorithm for multiprocessor servers. A particular focus of our work is to investigate practical issues in instantiating proportionatefair (P-fair) schedulers into conventional operating systems. We show via a simulation study that characteristics of conventional operating systems such as the asynchrony in scheduling multiple processors, frequent arrivals and departures of tasks, and variable quantum durations can cause proportionate-fair schedulers to become nonwork-conserving. To overcome this drawback, we combine DFS with an auxiliary work-conserving scheduler to ensure work-conserving behavior at all times. We then propose techniques to account for processor affinities while scheduling tasks in multiprocessor environments. We implement the resulting scheduler in the Linux kernel and evaluate its performance using various applications and benchmarks. Our experimental results show that DFS can achieve proportionate allocation, performance isolation and work-conserving behavior at the expense of a small increase in the scheduling overhead. We conclude that practical considerations such as work-conserving behavior and processor affinities when incorporated into a P-fair scheduler such as DFS can result in a practical approach for scheduling tasks in a multiprocessor operating system.

Enabling technologies in high speed communication and global process scheduling have pushed clusters of computers into the mainstream as general-purpose high-performance computing systems. More generality, however, implies more sharing and this raises new questions in the area of cluster resource management. In particular, in systems where the aggregate demand for computing resources can exceed the aggregate supply, how to allocate resources amongst competing applications is an important problem. Traditional solutions to this problem have focused mainly on global optimization with respect to system-centric performance metrics, metrics which ignore higher level user intent. In this paper, we propose an alternative market-based approach based on the notion of a computational economy which optimizes for user value. Starting with fundamental requirements, we describe an abstract architecture for market-based cluster resource management based on the idea of proportional resource sharing of...

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Shared-memory multiprocessors (SMPs) are being exten-sively used as general-purpose servers. The tight coupling of multiple processors, memory, and I/O provides enormous computing power in a single system, and enables the effi-cient sharing of these resources. The operating systems for these machines (UNIX or Win-dows NT) provide very few controls for sharing the resources of the system among the active tasks or users. This unconstrained sharing model is a serious limitation for a server because the load placed by one user can adversely affect other users ’ performance in an unpredictable manner. We show that this lack of isolation is caused by the resource allocation scheme (or lack thereof) carried over from single-user workstations. Multi-user multiprocessor systems require more sophisticated resource management, and we show how the proposed “performance isolation ” scheme can address the current weaknesses of these systems. We have implemented performance isolation in the Silicon Graphics IRIX operating system for three important system resources: CPU time, memory, and disk bandwidth. Running a number of workloads we show that our proposed scheme is success-ful at providing workstation-like isolation under heavy load, SMP-like latency under light load, and SMP-like throughput in all cases. 1.

This paper describes an algorithm, called Dynamic Window-Constrained Scheduling (DWCS), designed to meet the service constraints on packets from multiple, network-bound media streams with different performance objectives. Using only two attributes, a deadline and a loss-tolerance per packet stream, DWCS: (1) can limit the number of late packets over finite numbers of consecutive packets in loss-tolerant or delayconstrained, heterogeneous traffic streams, (2) does not require a-priori knowledge of the worst-case loading from multiple streams to establish the necessary bandwidth allocations to meet per-stream delay and lossconstraints, and (3) can exhibit both fairness and unfairness properties when necessary. In fact, DWCS can perform fair-bandwidth allocation, static priority (SP) and earliest-deadline first (EDF) scheduling. We show the effectiveness of DWCS using a streaming video application, running over ATM. 1 Introduction This paper describes a novel packet scheduling algorith...

In this thesis, we formalize the concept of an implicitly-controlled system, also referred to as an implicit system. In an implicit system, cooperating components do not explicitly contact other components for control or state information; instead, components infer remote state by observing naturally-occurring local events and their corresponding implicit information, i.e., information available outside of a defined interface. Many systems, particularly in distributed and networked environments, have leveraged implicit control to simplify the implementation of services with autonomous components. To concretely demonstrate the advantages of implicit control, we propose and implement implicit coscheduling, an algorithm for dynamically coordinating the time...

In this paper, we argue that conventional operating systems need to be enhanced with predictable resource management mechanisms to meet the diverse performance requirements of emerging multimedia and web applications. We present QLinux---a multimedia operating system based on the Linux kernel that meets this requirement. QLinux employs hierarchical schedulers for fair, predictable allocation of processor, disk and network bandwidth, and accounting mechanisms for appropriate charging of resource usage. We experimentally evaluate the efficacy of these mechanisms using benchmarks and real-world applications. Our experimental results show that (i) emerging applications can indeed benefit from predictable allocation of resources, and (ii) the overheads imposed by the resource allocation mechanisms in QLinux are small. For instance, we show that the QLinux CPU scheduler can provide predictable performance guarantees to applications such as web servers and MPEG players, albeit at the expense of increasing the scheduling overhead from 1 s to 4 s. We conclude from our experiments that the benefits due to the resource management mechanisms in QLinux outweigh their increased overheads, making them a practical choice for conventional operating systems.