KernelTrap: Discussions on Real Time

Real Time Kernel Prototype

“Sven-Thorsten Dietrich for MontaVista announced a set of
patches that he called ‘prototype real-time (RT) enhancements to
the Linux 2.6 kernel.’ The enhancements are a collection of
features integrated together, including Ingo Molnar’s voluntary
preemption and BKL mutex patches, and a mutex abstraction layer for
implementing spinlocks with mutexes. Sven explains, ‘the purpose of
this effort is to to further reduce interrupt latency and to
dramatically reduce task preemption latency in the 2.6 kernel
series. Our broad objective is to achieve preemption latency
bounded by the worst case IRQ disable.’ He goes on to add, ‘our
objective is to enable the Linux 2.6 kernel to be usable for
high-performance multi-media applications and for applications
requiring very fast, task level reliable control functions…'”


Realtime Preemption

“Since his first announcement of voluntary kernel preemption,
Ingo Molnar has continued to work on reducing overall latencies in
the kernel. His latest -T4 patch introduces a new kernel
configuration option about which he says, ‘the big change in this
release is the addition of PREEMPT_REALTIME, which is a new
implementation of a fully preemptible kernel model’ in which
‘spinlocks and rwlocks use semaphores and are preemptible by
default,’ and ‘the _irq variants of these locks do not disable
interrupts but rely on IRQ threading to exclude against interrupt