Composite is an Operating System (OS) with a focus on reliability, predictability, security, and flexibility. System policies, abstractions, and mechanisms are defined and implemented as user-level components. Components are hardware isolated from each other and execute at user-level thus increasing both system reliability and security. The component graph to the right is a component-based web-server.

A few of the research focuses of Composite include:

• HiRes. CPU, Memory, and I/O resources are managed hierarchically in Composite. This system for Hierarchical Resource management called HiRes enables individual subsystems to customize fundamental resource management policies efficiently and predictably while also isolating different subsystems from each other. A web-server might customize its scheduling and I/O management policies, while a data-base uses specialized memory management policies. Fine grained resource control is maintained, while ensuring isolation between subsystems. As opposed to Exokernels that place all resource management in processes, and monolithic kernels that place management in the single kernel, HiRes enables components to define the appropriate hierarchy for the system's goals.
• Memory Scheduling. We are investigating manipulating a form of memory in Composite called transient memory. This dynamically allocated memory simply has a bounded interval between allocation and deallocation. Transient memory enables memory to be dynamically added and removed from specific applications and scheduled throughout the system, while meeting application end-to-end constraints (i.e. deadlines). By intelligently shuffling memory around the system, we show that -- without swapping -- you can significantly increase the amount of usable system memory even in embedded systems.
• User-level Scheduling. The kernel includes no policies, instead implementing them in user-level components. Thus system policies including those for low-level resource management are redefinable, and isolated. The Composite kernel does not have a scheduler. Scheduling policies and synchronization protocols are defined by user-level schedulers. They can be replaced, and redefined for specific systems and applications -- a useful capability in real-time and embedded systems. Additionally, faults in other parts of the system, or in the scheduler itself will not propogate to the rest of the system. To enable efficient and predictable component-based scheduling, special care is taken to ensure accurate accountability, and low overhead for interrupt scheduling.
• Mutable Protection Domains. To maintain high isolation, invocations between components require IPC, which causes some overhead. The web-server makes between 50-70 IPCs to serve a webpage. Composite supports Mutable Protection Domains (MPD), which enables the system to dynamically construct and remove protection domain boundaries between components in response to where communication (IPC) overheads exist. Using MPD with the webserver, we increase performance by 40% while removing only 15% of the protection boundaries. MPD enables the system to optimally trade-off fault isolation for performance.
• Secure Bulletin Board System. Composite was used in the verifiable election based on Scantegrity for Takoma Park, MD. It provided a secure webpage for verifying ballots after the election.
• Current research in progress includes how to design a system to fundamentally support the unique characteristics of massively multi-core systems, and system designs for predictable fault recovery from low-level OS faults.

See our github page.

Reference Material