[vdr] Re: Kernel-Patch to make VDR undisturbable

[Andreas Schultz <aschultz@cs.uni-magdeburg.de>]

Hi,

On Monday 08 April 2002 16:44, Markus Dahlweid wrote:
> Werner wrote:
> >have a look at the LAD Homepage (Linux Audio Developer):
> >      /www.linuxdj.com/audio/lad
> >They have same problem (and a solution): "Low Latency" patches to
> >the linux kernel:
> >      http:/www.linuxdj.com/audio/lad/resourceslatency.php3
>
> If you are installing the "Low Latency Patch" I would also recommend
> using the "Preemptive Patch". The combination of both patches
> "guarantees" a response time of <2ms. Without those patches, the latency
> can easily be more than 100ms.

Let me answer both post in one:

This is all very interresting and it will improve things, but IMHO does *NOT* 
really help us. Why? Because all the mentioned patches deal with scheduling 
latency. They are designed to give you scheduling latencies < 3ms and we 
don't really need that.
In the DVB datastream, audio samples are usally around 32ms and a single 
frames is arround 40ms. The 1MB buffer we use, appears to hold about 500ms 
worth of audio and video data. The dvb cards buffer apparently also hole 
something of arroung 100ms (just a guess) of data. A scheduling latency of 
lets say 100ms will therefore hardly affect us. Normal rt scheduling on a 
stock linux kernel will give us latencies that are somewhat smaller than 
that.
What we would need is a guaranteed disk I/O rate, and this is something i 
haven't found yet.

Yet, i might be wrong, so i'm going to try them anyway.....

Andreas