[Asterisk-Users] zaptel PRI drivers

[Peter Svensson]

On Sun, 20 Mar 2005, Tom wrote:

> I have a quick question.
> I know that running X on an asterisk server is not officially "supported",
> however, I've never had any trouble with it until now (8 months, using wctdm
> cards with fxo and fxs ports, IAX trunks, SIP phones, everything except a PRI
> card).  Now I just installed my first asterisk box that terminates a PRI, and
> bam, HDLC errors up the wazoo if X is running, if its not, everything is fine,
> I assume this is because the timing parameters for the PRI are so much more
> strick.
> 
> I don't mind if X is a little less responsive (even alot less responsive), but I
> would really like to be able to run X on a server with a PRI.  Is there any way
> to reduce X11's priority so that it doesn't interfere with the zaptel driver
> for the PRI... I've tried renicing X as far down as I can and renicing Asterisk
> up as far as I can, however I fear this won't ever fix the problem since I
> think the actual kernel module that is running the pri card needs to get higher
> priority (ie, the kernel itself needs higher priority).  Is there any way to do
> this?  Am I correct in my analysis?  I really don't understand why on a system
> that averages less than 3% CPU usage with X running, why it can't handle the
> PRI.  I know for whatever reason X always gets a really high priority (although
> top doesn't show X getting any special treatment its PR 15 NICE 0 by default,
> lower than most other processes on the system).

The graphics drivers run party in kernel mode and are thus not under the 
regular control of the user level scheduler. The user level scheduler is 
the only place nice has any effect.

All may not be lost. Under Linux 2.6 there is an experimental patch to 
make the kernel preemtable. This allows various parts of the kernel to 
yeild control to other parts on short notice. With the most aggressive 
settings the patch is reported to bring latency down to a far better level 
than would be required by the Zaptel cards.

It is experimental though and probably best left away from a production 
machine. On a testing machine it would be very interesting. Eventually 
this is how everyone will use the zaptel cards so an early preview is 
interesting.

Peter