A logical partition in an IBM pSeries TM symmetric multiprocessor (SMP) system is a subset of the hardware of the SMP that can host an operating system (OS) instance. Dynamic reconfiguration (DR) on these logically partitioned servers enables the movement of hardware resources (such as processors, memory, and I/O slots) from one logical partition to another without requiring reboots. This capability also enables an autonomic agent to monitor usage of the partitions and automatically move hardware resources to a needy OS instance nondisruptively. Today, as SMPs and nonuniform memory access (NUMA) systems become larger and larger, the ability to run several instances of an operating system(s) on a given hardware system, so that each OS instance plus its subsystems scale or perform well, has the advantage of an optimal aggregate performance, which can translate into cost savings for customers. Though static partitioning provides a solution to this overall performance optimization problem, DR enables an improved solution by providing the capability to dynamically move hardware resources to a needy OS instance in a timely fashion to match workload demands. Hence, DR capabilities serve as key building blocks for workload managers to provide selfoptimizing and self-configuring features. Besides dynamic resource balancing, DR also enables Dynamic Capacity Upgrade on Demand, and self-healing features such as Dynamic CPU Sparing, a winning solution for users in this age of rapid growth in Web servers on the Internet.One of the cardinal features of an autonomic component in an information technology (IT) infrastructure is the ability of the component to adapt itself smoothly to changes in its environment. Endowing a computing system with this self-management feature often translates to the implementation of selfprotecting, self-healing, self-optimizing, and self-configuring algorithms and subcomponents. Because the primary role of an operating system (OS) is to manage the physical resources of a computer system so as to optimize the performance of its applications (including middleware, which consists of applications from the perspective of the OS), an OS supporting autonomic computing 1 needs to handle the changes in the amount of physical resources allocated to it in a smooth fashion. Some of the most prominent physical resources of an OS are processors, physical memory, and I/O devices.The current tendency among the noncommodity symmetric multiprocessor (SMP) system vendors is to develop systems that are increasingly large in terms of the number of processors, number of I/O slots, and memory size. Although advances in the design of hardware continue to provide rapid increases in the

This paper studies the effects that dynamic reconfiguration (DR) has on a WebSphere workload while CPUs are dynamically added to and removed from the underlying AIX instance. DR is a new technology available in AIX 5.2. This study shows that the resource allocations for a complex and function-rich middleware system such as WebSphere can be efficiently and dynamically managed by the DR technology, without WebSphere having to explicitly accommodate for the DR features of the operating system.

This paper investigates the changes in AIX behavior, or the lack of them, and the resulting performance impact from a generational change in servers in a typical large scale eCommerce application environment without extensive tuning of the OS and the application stack for the changing hardware.We have investigated the performance and impediments to performance at the microprocessor level and at the OS level. This paper dissects the performance data as observed from the OS and from hardware performance counters, and suggests areas for further improvements.

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