Real time kernel exploitation

Alessio Igor Bogani abogani at ubuntu.com
Mon Aug 11 16:09:23 BST 2008


Hi,

I suggest a simple hack that result in a better system response on
audio related tasks. This hack is based on one of the most important
real time kernel feature: IRQ threaded. For this reason it works only
on this type of kernel.

Prioritizing IRQs reduce possibility of X-Runs happens. As far i know
it the most frustrating event for an UbuntuStudio users.


Let's start with a proof of concept!

A script like this called during boot do the dirty work:

*** /etc/init.d/setirqprio ***
#!/bin/sh

# PRIOVALUE is stored into /etc/default/setirqprio

. /etc/deafult/setirqprio

for irqpath in $(ls /sys/class/sound/card[0-9]/device/irq)
do
   irq=$(cat $irqpath)
   pid=$(pidof IRQ-$irq)
   chrt -p $PRIOVALUE $pid
done
*****************************

As you can see this script increase (to 75) the priority of IRQs of
the all sound cards present in the pc.

Obviously we should place setirqprio into /etc/event.d/ directory, add
capability to turn it on/off and put /etc/default/setirqprio under ucf
to do a great work.

Ciao,
Alessio



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