Collaborative Research: Progress-Based Resource Management Using Control

数字革命的一个结果是，通用计算机正被应用于越来越广泛的应用领域。然而，缺乏合适的操作系统支持仍然是将COTS（现成商品）计算机应用于许多这些应用领域的主要障碍，特别是那些正确性对时间或速率敏感的应用领域。现有操作系统中缺少的一个重要特性是能够根据应用程序的需要为应用程序分配资源。需要这个特性来防止一个应用程序影响另一个应用程序的正确性，例如发生优先级反转，并且在面对资源过度订阅和应用程序需求随时间变化的情况下实现近乎最优的资源分配。Steere和Walpole介绍了一种新的资源管理方法，即基于进度的资源管理，它根据感知到的需求将资源分配给应用程序。调度器监视应用程序的进度，将这些测量值与应用程序的期望速率进行比较，并增加或减少应用程序的分配，以将其实际速率驱动到期望值。原型机的初步经验是有希望的。CPU分配器使用反馈控制器（低通滤波器后面跟着PID控制器）通过动态改变管道线程的保留风格分配来调节多媒体管道中的缓冲区填充级别。他们还使用相同的方法在终端主机包调度程序中分配网络带宽。他们使用这些原型的经验表明，他们强烈需要更正式的建模和分析。原型很难正确调整；因为正确的性能取决于控制器的参数设置和应用程序的行为，这是可以改变的。此外，自适应应用程序（如自适应QoS）的存在可能导致原本稳定的系统出现振荡或发散。标准的计算机科学形式化方法不能帮助人们理解系统的自适应行为，因为它们关注的是接口语法和语义。我们所需要的是理解动态系统随时间变化的行为的分析技术，例如在控制系统中使用的分析技术。同时，将控制风格的建模和分析应用于软件系统本身就是一个研究挑战。软件系统本质上是离散的，人们不仅要考虑数据值采样和表示的量化误差，还要考虑底层信号本身的量化误差。此外，诸如管道之类的软件应用程序争用对托管资源（如CPU和内存）的访问，也争用对非托管资源（如同步变量（锁和信号量））的访问。这些同步问题使得很难预测一个资源分配变化的影响，因此很难为该资源设计一个控制器。

A consequence of the digital revolution is that general purpose computers are being applied to an ever increasing range of applications. However, lack of suitable operating system support remains a key obstacle in applying COTS (commodity-off-the-shelf) computers to many of these application domains, particularly those whose correctness is time- or rate-sensitive. One important feature that is missing in existing operating systems is the ability to assign resources to applications based on application need. This feature is needed to prevent one application from affecting the correctness of another, such as occurs in priority inversion, and to achieve near-optimal resource allocation in the face of oversubscription of resources and changes in application need over time.Steere and Walpole introduced a novel approach to resource management, progress-based resourcemanagement, that allocates resources to applications based on perceived need. The scheduler monitors anapplication's rate of progress, compares these measurements with the application's desired rate, andincreases or decreases the application's allocation to drive its actual rate to its desired value. Initial experi-ence with prototypes is promising. A CPU allocator uses a feedback controller (low-pass filter followed bya PID controller) to regulate buffer fill levels in a multimedia pipeline by dynamically changing reservation style allocations of the pipeline threads. They have also used the same approach to allocate network bandwidth in an end-host packet scheduler.Their experience with these prototypes indicates a strong need for more formal modeling and analysis. The prototypes are difficult to tune correctly; since correct performance depends both on the controller's parameter settings and the behavior of the application, which can change. In addition, the presence of adaptive applications (such as adaptive QoS) can lead an otherwise stable system to oscillate or diverge. Standard computer science formal methods do not help one to understand a system's adaptive behavior, since they focus on interface syntax and semantics. What is needed is analytical techniques for understanding the behavior of a dynamic system over time, such as those used in control systems.At the same time, applying control-style modeling and analysis to software systems is itself a research challenge. Software systems are discrete by nature, and one must consider quantization error not only in sampling and representation of data values but also in the underlying signal itself. In addition, software applications such as pipelines contend for access to managed resources such as CPU and memory but also to unmanaged resources such as synchronization variables (locks and semaphores). These synchronization issues make it difficult to predict the effect of a change in allocation for one resource, and hence to design a controller for that resource.