Casuar - A Protected Library OS for running Windows applications on top of Vortex

Abstract

Today, virtual machines (VMs) are commonly employed to encapsulate and isolate workloads in the cloud, enabling efficient utilization of hardware resources through the use of statistical multiplexing. Still, there is a significant overhead associated with the use of VMs; each VM instance has to contain a complete OS environment to support the execution of applications that are dependent on the specific services provided by that OS. Ultimately, this has led to the development of alternate, more light-weight approaches to virtualization.

A library OS trades isolation for performance, by allowing applications to execute natively on a host rather than inside a VM. All necessary OS abstractions are provided through user-mode libraries that run as part of the address space of each application. This commonly results in smaller resource footprints and better performance for applications. However, there are a few drawbacks to the library OS approach. First, it is either costly or difficult to enable sharing between multiple processes. Second, application compatibility can only be achieved at a higher level than the application binary interface (ABI), unless applications are modified to exploit alternate interfaces.

The protected library OS (PLOS) is a novel architectural abstraction that is similar to the traditional library OS, but also facilitates hosting of multi-process applications, and uses virtualization technology to target compatibility at the ABI level. It has already been demonstrated as a promising architecture, through the implementation of a PLOS that mimics the Linux 3.2.0 kernel, capable of running complex, unmodified Linux applications like Apache, MySQL, and Hadoop.

This thesis presents Casuar—a new PLOS that targets compatibility with Windows applications. By implementing a subset of the core OS services provided by the Windows NT kernel, we have been able to run Native applications and system DLLs on both Windows and Casuar. We evaluate the performance of Casuar experimentally, by comparing the system to native Windows and Wine through a series of micro-benchmarks. Our results show that Casuar attains near-native performance for a number of system services, and in many cases significantly outperforms Wine.