Shared Memory Input Queue

Shared Memory Input Queue

A shared memory input queue (called a shmiq in Silicon Graphics code comments, and pronounced "shmick") is a fast way of receiving input device events by eliminating the filesystem overhead to receive data from input devices. Instead of the X server reading the input devices through file descriptors, a kernel-level driver deposits input events directly into a region of the X server's address space, organized as a ring buffer.

The IRIX shmiq device driver is implemented as a STREAMS multiplexor. This allows an arbitrary number of input sources (in the form of STREAMS modules) to be linked to it so all input sources are funneled through the shmiq.

In addition to processing input events from input device modules, the schmiq driver also processes events from the graphics subsystem, and updates the screen cursor position. This allows smooth cursor movement since cursor positioning is done in kernel code, without Xsgi involvement.