Re: [tlug] timing for geeks II.

[Jim <jep200404@example.com>]

On Mon, 19 Dec 2005 10:05:58 +0900 Josh Glover <jmglov@example.com> wrote:

> Linux has a real-time scheduler, but I have not used it. 

Linux is _nibbling_ on real-time stuff. 
Linux has made huge strides in real-time-ish performance, 
but Linux is not a genuine real-time operating system (yet). 

With real-time OSs there is hard real-time and soft real-time. 
Hard real-time is when there are iron glad time guarantees. 
Soft real-time is for when the time goals are met _almost_ 
all of the time. 

Linux is not hard real-time, and does not pretend to be. 
It is nibbling at becoming soft real-time. This seems to 
have been pushed by audio folks as much as the expected 
industrial folks. 

The main way to do hard real-time stuff with Linux 
is for the hard real-time stuff to run in a layer 
_above_ Linux, and for the Linux OS to run essentually as 
a low priority application/task, which can be 
pre-empted by the non-Linux hard real-time code that has 
guaranteed response times. Communicating between 
the non-Linux hard real-time code and the real Linux 
non-real-time code is fun.