Chapter 6. Realtime Support in Linux

Table of Contents
Virtual Memory
Shared Memory
High Resolution POSIX Timers (HRT)
Realtime Signals
POSIX Asynchronous I/O
POSIX Threads
Quality of Service


From the very first versions of Linux, the scheduler was realtime POSIX compatible. It supports, among others, the fixed priority (SCHED_FIFO) policy, which is the base feature to build a realtime systems. It also provides the POSIX required: SCHED_RR and SCHED_OTHER. The range of priorities is [0..99].

A lot of work has been done to improve the performance of the scheduler through a careful design which yield to a new scheduler code and structure. Next stable Linux kernel (2.4.19), as well as unstable kernel development (2.5.x), will replace the old scheduler code with an improved "O(1) scheduler" developed by Ingo Molnar . This new scheduler is able to manage a large number of processes with no overhead degradation.