[linux-audio-dev] [Slightly OT] How to access "real-time" capabilities

[Asbjørn Sæbø]

This is, I know, slightly off-topic for this group, as it does not deal 
with audio per se.  It does, however, deal with the 
"real-time"/preemptible Linux kernel, for which I think most of the 
expertice is gathered here.


The OS is Linux, the computer an ordinary PC. The task we are faced with
is to run a program, tcpreplay, in such a way that it delivers its
network packets as precisely as possible.  I.e. the packets should be
delivered to the network with the smallest possible timing error.

We think that the way to minimize this timing error is to use a kernel 
with the real-time patches, as this will improve latency and response 
times.

The question is how we can assure that the program really utilizes the 
real-time capabilities of the kernel.  My understanding is that having a 
real-time capable kernel is only the first step, the second necessary 
step is to get access to this capabilities?  So, how does one accomplish 
this, given that the program itself does nothing to achieve this?


* Will an ordinary program, run as root, take advantage of the real time 
  capabilities of the kernel?
* Will an ordinary program, run as a user that is a member of the 
  "audio" group on f.i. Agnula, take advantage of the real-time capabilities?
* If given a real-time kernel, what else is necessary to take advantage 
  of its capabilities?
* How does normal priorities (nice, renice) play together with the 
  real-time kernel?


With kind regards
Asbjørn Sæbø