MicroXwin

MicroXwin

Developer(s)	DSPSOFT INC
Stable release	2.3 / July 25, 2011; 3 months ago (2011-07-25)
Operating system	Unix-like
Available in	English
Type	Windowing system
License	Hybrid. Proprietary license for the kernel module and BSD style license for the rest
Website	microxwin.com

MicroXwin is a windowing system similar to the X Window System (simply known as X). By a different architecture, it provides a faster graphical user interface backend than the original X Window System, while still preserving the compatibility with standard X11 applications. It also greatly reduces the size needed by the system in memory and disk resource usage.

Background

The GUI of the X Window System is slower partly because it is designed in a client–server model. X is separated into two parts, the X server and multiple X clients. The X server is a single-threaded process which handles the requests from X clients to perform access and control to graphical and input devices. Some drawbacks have been noticed in this kind of configuration:

1. There is a round-trip delay time between client and server (latency rather than from the protocol itself) when a synchronized request is issued.
2. A context switch is required to move between executing client code and server code, if they are running on the same machine.
3. The client and server have to buffer and format commands and responses as per the X Window protocol.
4. On processors with virtually addressed cache, such as ARM 9, context switching between an application and the X server results in a cache flush, further degrading performance.

Due to higher CPU usage, these drawbacks make the X Window System an unresponsive and slower GUI framework to the user in comparison with other windowing systems such as Microsoft Windows (up to and including Windows XP) and Quartz.

Advantages

By contrast, the client–server architecture is abandoned in the design of MicroXwin. In MicroXwin, the X server is replaced by a kernel module x11.ko in the OS and dedicated libraries, LibX11.so and LibXext.so, compatible with Xlib and are used by the X clients to interact with the kernel module. By the configuration, MicroXwin provides the following advantages:

1. An improvement of 62% for asynchronous display or 384% for synchronous display of images of a 100x100 size.
2. Scrolling a web page under MicroXwin is much faster and smoother.
3. There are only about 300 Kbytes of kernel memory in use by the kernel module. X.Org server, however, has a run-time memory usage of 12MB.
4. The smallest MicroXwin distribution can fit within 1 megabyte of disk space in contrast to the X.Org Server, which has a disk footprint of 1.8MB.

Rationale for advantages

1. Round trip and synchronized requests are even faster on MicroXwin.
2. The round trip delay measured is much smaller.
3. Kernel module x11.ko has higher priority than the user-space X server.
4. Performance is independent of scheduling latency caused by the scheduler, because the X server is no longer a process in the system.

Drawbacks

MicroXwin is more suitable as the GUI for an embedded system which is usually required to perform real-time tasks. However, there are still drawbacks that can easily be observed in this architecture:

1. Network transparency no longer exists. X clients cannot connect to a remote terminal running MicroXwin without extra work.
2. The library needs to be updated each time Xlib is changed in order to maintain compatibility.
3. The additional kernel module x11.ko may crash the system if it is not well-designed or stable.

In addition to the above drawbacks, shape extension is not supported before version 1.5. MicroXwin supports the shape extension starting from version 1.5.

See also

• Wayland - lightweight replacement for the X Window System
• Windowing system
• X Window System

References

• Hania Gajewska, Mark S. Manasse and Joel McCormack, Why X Is Not Our Ideal Window System (PDF), Software — Practice & Experience vol 20, issue S2 (October 1990)

External links

• MicroXwin official website

• Comparison of X Window System and MicroXwin architectures

• MicroXwin Performance on OMAP1710 (OMAP1710, a microprocessor that Nokia 770 based on) (in DOC format)
• MicroXwin: 針對嵌入式系統的高效能 X Window System 實作