Virtualization has become an important technology that is used across many platforms, particularly servers, to increase utilization, multi-tenancy and security. Virtualization introduces additional overhead that often relates to memory management, interrupt handling and hypervisor mode switching. Among those, memory management and translation lookaside buffer (TLB) management have been shown to have a significant impact on the performance of systems. Two principal mechanisms for TLB management exist in today's systems, namely software and hardware managed TLBs. In this paper, we analyze and quantify the overhead of a pure software virtualization that is implemented over a software managed TLB. We then describe our design of hardware extensions to support virtualization in systems with software managed TLBs to remove the most dominant overheads. These extensions were implemented in the Power embedded A2 core, which is used in the PowerEN and in the Blue Gene/Q processors. They were used to implement a KVM port. We evaluate each of these hardware extensions to determine their overall contributions to performance and efficiency. Collectively these extensions demonstrate an average improvement of 232% over a pure software implementation.

The three major solutions for increasing the nominal performance of a CPU are: multiplying the number of cores per socket, expanding the embedded cache memories and use multi-threading to reduce the impact of the deep memory hierarchy. Systems with tens or hundreds of hardware threads, all sharing a cache coherent UMA or NUMA memory space, are today the de-facto standard. While these solutions can easily provide benefits in a multi-program environment, they require recoding of applications to leverage the available parallelism. Threads must synchronize and exchange data, and the overall performance is heavily in influenced by the overhead added by these mechanisms, especially as developers try to exploit finer grain parallelism to be able to use all available resources.

The cost and operational complexity of traditional High Availability solutions has limited their widespread adoption. Virtualization allows availability properties to be associated with the system architecture, rather than depending on the intrinsic reliability of components. This paper introduces an extensible grammar that classifies the states and transitions of virtual machine images. From this grammar, rules for recovery and High Availability can be created which define how virtualization allows for simplified fault tolerance, making HAVENs accessible to the mainstream user.

Designing and implementing system software so that it scales well on shared-memory multiprocessors (SMMPs) has proven to be surprisingly challenging. To improve scalability, most designers to date have focused on concurrency by iteratively eliminating the need for locks and reducing lock contention. However, our experience indicates that locality is just as, if not more, important and that focusing on locality ultimately leads to a more scalable system. In this paper, we describe a methodology and a framework for constructing system software structured for locality, exploiting techniques similar to those used in distributed systems. Specifically, we found two techniques to be effective in improving scalability of SMMP operating systems: (i) an object-oriented structure that minimizes sharing by providing a natural mapping from independent requests to independent code paths and data structures, and (ii) the selective partitioning, distribution, and replication of object implementations in order to improve locality. We describe concrete examples of distributed objects and our experience implementing them. We demonstrate that the distributed implementations improve the scalability of operating-system-intensive parallel workloads.

K42 is one of the few recent research projects that is examining operating system design structure issues in the context of new whole-system design. K42 is open source and was designed from the ground up to perform well and to be scalable, customizable, and maintainable. The project was begun in 1996 by a team at IBM Research. Over the last nine years there has been a development effort on K42 from between six to twenty researchers and developers across IBM, collaborating universities, and national laboratories. K42 supports the Linux API and ABI, and is able to run unmodified Linux applications and libraries. The approach we took in K42 to achieve scalability and customizability has been successful.The project has produced positive research results, has resulted in contributions to Linux and the Xen hypervisor on Power, and continues to be a rich platform for exploring system software technology. Today, K42, is one of the key exploratory platforms in the DOE's FAST-OS program, is being used as a prototyping vehicle in IBM's PERCS project, and is being used by universities and national labs for exploratory research. In this paper, we provide insight into building an entire system by discussing the motivation and history of K42, describing its fundamental technologies, and presenting an overview of the research directions we have been pursuing.