[[UbuntuStudio/audio-settings | ../UbuntuStudio/audio-settings]]

Discussion about kernels and kernel configurations here..

== Kernel Testing ==

=== Building your own kernel ===

A short description of how to build a kernel for testing.

= linux-lowlatency =

Shipped with Ubuntu Studio since 12.04 Precise. Principally a standard Ubuntu kernel (no additional patches to the code, allthough the linux-lowlatency shipped with precise includes a minor patch). 

== Configurations of interest for linux-lowlatency ==

These configs need to be somewhat documented and tested

=== To enable low latency (needs to be expanded) ===

 * '''[[http://cateee.net/lkddb/web-lkddb/PREEMPT.html | CONFIG_PREEMPT]]'''
  * ''conflicts with:'' '''[[http://cateee.net/lkddb/web-lkddb/PREEMPT_NONE.html |CONFIG_PREEMPT_NONE]]'''
  * ''conflicts with:'' '''[[http://cateee.net/lkddb/web-lkddb/PREEMPT_NONE.html | CONFIG_PREEMPT_VOLUNTARY]]'''

To enable this option edit the config file to have these line read:

{{{{
CONFIG_PREEMPT=y
# CONFIG_PREEMPT_NONE
# CONFIG_PREEMPT_VOLUNTARY
}}}}

'''May reduce latency'''
 * '''[[ http://cateee.net/lkddb/web-lkddb/PREEMPT_RCU.html | CONFIG_PREEMPT_RCU ]]'''

{{{
CONFIG_PREEMPT_RCU=y
}}}

''additional, related configs''

 * '''[[http://cateee.net/lkddb/web-lkddb/TREE_PREEMPT_RCU.html | CONFIG_TREE_PREEMPT_RCU]]'''
 * '''[[http://cateee.net/lkddb/web-lkddb/RCU_BOOST.html | CONFIG_RCU_BOOST]]'''
 * '''[[http://cateee.net/lkddb/web-lkddb/RCU_CPU_STALL_DETECTOR.html | CONFIG_RCU_CPU_STALL_DETECTOR]]'''
 * '''[[http://cateee.net/lkddb/web-lkddb/RCU_CPU_STALL_VERBOSE.html | CONFIG_RCU_CPU_STALL_VERBOSE]]'''

as configure in current -lowlatency..
{{{
CONFIG_TREE_PREEMPT_RCU=y
# CONFIG_RCU_BOOST is not set
# CONFIG_RCU_CPU_STALL_DETECTOR is not set
# CONFIG_RCU_CPU_STALL_VERBOSE is not set
}}}

=== To enable the use of the rtirq script to change rtprio for devices: ===

this enables the use of ''threadirqs'' as a kernel boot parameter
 * '''[[http://cateee.net/lkddb/web-lkddb/IRQ_FORCED_THREADING.html | CONFIG_IRQ_FORCED_THREADING]]'''

optionally, to make ''threadirqs'' a default boot parameter
 * '''[[http://cateee.net/lkddb/web-lkddb/CMDLINE.html | CONFIG_CMDLINE]]'''
  * ''depends on:'' '''[[http://cateee.net/lkddb/web-lkddb/CMDLINE_BOOL.html | CONFIG_CMDLINE_BOOL]]'''

To enable these options edit the config file to have these line read:
{{{{
IRQ_FORCED_THREADING=y
CONFIG_CMDLINE="threadirqs"
CONFIG_CMDLINE_BOOL=y
}}}}

===  High resolution timer: ===

(Not exactly sure which of CONFIG_HZ=1000 and CONFIG_HZ_1000=y depend on which. )
 * '''[[http://cateee.net/lkddb/web-lkddb/HZ_1000.html | CONFIG_HZ_1000]]'''
 * '''[[http://cateee.net/lkddb/web-lkddb/HZ.html | CONFIG_HZ]]'''
  * ''depends on:'' '''[[http://cateee.net/lkddb/web-lkddb/NO_HZ.html | CONFIG_NO_HZ]]'''

to enable high resolution timer
{{{
CONFIG_HZ_1000=y
CONFIG_HZ=1000
# CONFIG_NO_HZ is not set
}}}

(optionally, tickless timer - add the config here) 

=== Need to be investigated ===

 * '''[[http://cateee.net/lkddb/web-lkddb/NTP_PPS.html | CONFIG_NTP_PPS]]'''
 * '''[[http://cateee.net/lkddb/web-lkddb/SLAB.html | CONFIG_SLAB]]'''
 * '''[[http://cateee.net/lkddb/web-lkddb/PREEMPT_NOTIFIERS.html | CONFIG_PREEMPT_NOTIFIERS]]'''
 * '''[[[ http://cateee.net/lkddb/web-lkddb/EXPERT.html | CONFIG_EXPERT]]'''
 * '''[[http://cateee.net/lkddb/web-lkddb/PREEMPT_TRACER.html | CONFIG_PREEMPT_TRACER]]'''
 * '''[[http://cateee.net/lkddb/web-lkddb/DEBUG_KERNEL.html | CONFIG_DEBUG_KERNEL]]'''

as used in current -lowlatency
{{{
# CONFIG_NTP_PPS is not set
CONFIG_SLAB=y
CONFIG_PREEMPT_NOTIFIERS=y
# CONFIG_EXPERT is not set
# CONFIG_PREEMPT_TRACER is not set
# CONFIG_DEBUG_KERNEL is not set 
}}}

== Additional configs ==

* [[http://cateee.net/lkddb/web-lkddb/RT_GROUP_SCHED.html | CONFIG_RT_GROUP_SCHED]]

== linux-rt ==

Not in Ubuntu repo since 9.10 Karmic.