Preemption concepts, Rhealstone benchmark and scheduler analysis of linux 2.4

In this paper we examine the soft realtime capabilities of the Linux kernel 2.4 and realtime enhancements. We discuss and visualize in the form of PDLT (process dispatch latency time) diagrams how the MontaVista Preemption Patch 6 for Linux 2.4.2 preempts a Linux system call executing in kernel mode. In similar diagrams we show the effect of introducing Conditional Preemption Points, like Ingo Molnar´s and Andrew Morton´s Low Latency Patches do. To detect possible performance changes we measure some programs of the Rhealstone Benchmark on Linux kernels and variants. We examine the behaviour of the Linux scheduler when scheduling a SCHED FIFO process varying the number of SCHED OTHER load processes ready to run.