Regarding PREEMPT_RT option

[Sabree Blackmon]

If you haven't already run into it:
https://rt.wiki.kernel.org/index.php/Main_Page

In a high level sense, the option compiles the Linux kernel so that certain
kernel operations can be preempted - in other words the kernel can be told
to wait while another higher priority task needs to be completed. This is
useful we you need to handle time sensitive tasks, like handling precision
timers or hardware interrupts, timing sensitive device drivers, safety
critical programs, etc. The is especially useful in embedded applications,
or audio intensive application where low latency is required.

If you do a search for "Real Time Linux", you will find a lot more
information. Linux with the preemptive patch applied is often called a "real
time" operating system. "Real time" in a basic sense means "very low
latency". "Hard real time" OS's, like eCos, freeRTOS, QNX, allow the most
basic kernel operations to be preempted, useful for the most timing critical
operations were a few milliseconds in delay of an operation can mean system
failure or computational error. Linux with the preemptive option can be
considered a "soft real time" OS, meaning not all kernel operations can
preempted, if I'm not mistaken. There is however, a patch (
https://rt.wiki.kernel.org/index.php/CONFIG_PREEMPT_RT_Patch) that allows
Linux to behave in a more "hard real time" manner. The patch allows most
kernel operations to be preempted but not all.

If you need very low latency "hard real time" behavior with Linux, you can
use something like RTAI or Xenomai. These achieve hard real time performance
by running the Linux kernel as a child process to their own parent process,
allowing every task to be preempted if needed. Thus, RTAI and Xenomai are
also popular in embedded systems where the use of Linux is preferred, but
very low latency is required as well.

It's a lot of information, but hopefully you'll find it useful!

- Sabree Blackmon

On Wed, Feb 2, 2011 at 3:32 PM, Sri Ram Vemulpali
<sri.ram.gmu06 at gmail.com>wrote:

> Hi all,
>
>       I am trying to find detailed explanation of preemption option
> in config. For desktop, server, and low-latency desktop. Can anyone
> explain in what scenarios these are useful.
>
> Thanks in advance
>
>
> --
> Regards,
> Sri.
>
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