Enhancing MINIX 3.X input/output performance

Abstract

MINIX 3.X is an open-source operating system designed to be highly reliable, flexible, and secure. The kernel is extremely small and user processes, specialized servers and device driver runs as user-mode insulated processes. These features, the tiny amount of kernel code, and other aspects greatly enhance system reliability. The drawbacks of running device drivers in user-mode are the performance penalties on input/output ports access, kernel data structures access, interrupt indirect management, memory copy operations, etc.. As MINIX 3.X is based on the message transfer paradigm, device drivers must request those operations to the System Task (a special kernel representative process) sending request messages and waiting for reply messages increasing the system overhead. This article proposes a direct call mechanism that keeps system reliability running device drivers in user-mode but avoiding the message transfer, queuing, dequeuing and scheduling overhead