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

[Asbjørn Sæbø]

n Thu, Jun 09, 2005 at 01:11:39PM +0200, Florian Schmidt wrote:

> [on scheduling and real time]

> btw: i don't know if all this info helps you at all.

I found it helpful indeed.

> Why don't you tell us a bit more about your problem domain and we can
> try to figure out how/if RP kernels can help you with it..

The centre where I am working (<URL:http://www.q2.s.ntnu.no/ >) is doing
research on quality of service in communication services.

We have equipment ("DAG" cards) that enables us to capture network
packet streams with high accuracy.  (The packets are time stamped at
capture.) These streams may then be played back using tcpreplay on a
computer running Linux.

We would like this playback to reproduce the stream accurately, i.e.
with very accurate timing of the packets.  Testing has shown us that the
playback jitter is on the order of a couple of milliseconds (99 percent
of the packets are within +/- 2ms of correct timing). We would like to
improve that, and thought that a low-latency kernel might be suitable to
achieve this.

Judging from the answers so far, we should probably try using a 2.6.11
kernel first.  Using "chrt" on tcpreplay might be worth an attempt as a
"quick-and-dirty" solution.  And the "real" solution is probably to
rewrite tcpreplay.

Asbjørn
--
Asbjørn Sæbø, post.doc.
Centre for Quantifiable Quality of Service in Communication Systems
Norwegian University of Science and Technology
<URL: http://www.q2s.ntnu.no/ >