High-bandwidth services like audio, video, image processing, and three-dimensional graphics are at or coming soon to a desktop computer near you. Processors and graphics hardware continue to get faster. The increasing relative cost of cache misses, context-switching, and transport overhead give an advantage to greater system locality. Users desire slicker application appearances, better responsiveness, and seamless inter-application communication.
What should window systems do to stay current with these trends?
This paper proposes a restructuring of the industry standard X Window System [21]
to answer these trends.
This new window system architecture, called D11,
provides higher
performance local window system operations while preserving complete
compatibility with X11 clients and servers. The system utilizes a new
operating system facility similar in concept to the Unix kernel's
traditional implementation but designed for user-level execution. Local
D11 clients can execute within the D11 window system kernel without compromising
the window system's integrity. The transport of protocol is eliminated
for local window system interactions. Context switching and data
copying costs are minimized.
The name D11 refers not to a new revision of the X11 protocol; indeed D11 aims to obsolete the local use of the X11 protocol. D11 is a new window system architecture but fully X11 compatible. X11 programs can be trivially recompiled to utilize D11 since the full Xlib application programming interface (API) is retained by D11. Existing X11 clients will continue to work with the D11 window system by generating X11 protocol, and D11 clients will work with existing X11 servers by falling back to X11 protocol. D11 is not an extension or minor addition to X11. It is a reinvention of X11's fundamental architecture.
Section 2 motivates the new architecture for D11 by considering window system trends. Section 3 presents the means for better performance in D11. Section 4 contrasts D11 to other approaches. Section 5 describes the active context operating system facility that D11 utilizes. Section 6 considers the implementation of D11 and how to provide complete X11 compatibility in D11.