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This specification details the plan to add hard real time support in Ubuntu.


In some contexts (i.e. industrial automation, robotics and telco) the low-latency support is insufficient. In order to push Ubuntu in these contexts it is necessary to add support for high resolution timers and full preemption in the Linux kernel. These features have been implemented by Thomas Gleixner and Ingo Molnar (

Use cases

Alex is developing an application software (SCADA type) for a customer and he would be very happy to use Linux and Ubuntu for the deployment.


This specification covers a new linux kernel flavour (-rt) in Ubuntu.


We will use the new kernel build system created by the Ubuntu Kernel Team for Gutsy Release. More information about it.

Unresolved issues

1. High precision timers don't work on machine which have only PIT as souce clock more info
2. The realtime kernel could expose you to security issues
3. On some machine esd with realtime kernel freeze GNOME (please kill esd and relaunch it after)
4. Restricted modules could increase latencies (please buy only hardware which have a free driver!)

Packages available

Packages available in Gutsy archives:


Q) Did you manage to include all the regular Ubuntu kernel patches in it? If not, is it possible to know what was left out?
A) No i don't include anything because i use _only_ full Ubuntu Kernel (not vanilla, not custom version or other). Ubuntu Realtime kernel is Ubuntu kernel plus realtime preemption patch. Also the configuration (aka /boot/config*) is the same expects for specific realtime options.

Q) Where can I find documentation?
A) All existing docs are available on

Q) Which are the differences with vanilla Ingo Molnar's patch?
A) A simple adaptation to the BenC's kernel git tree isn't the only difference: We work on Ubuntu specific code or drivers (aka linux-ubuntu-modules) and also remove all code which isn't strictly related to realtime preemption support (in example kvm/paravirt/hypercall). In order to be more precise these are included:

Q) What features are included in Ubuntu rt kernel flavour?
A) Completely Fair Scheduler
Spinlocks are replaced by realtime mutexes with priority inheritance
Interrupt handling threads
Preemptible RCU

BoF agenda and discussion

  • Any suggestions/feedbacks/requests? Alessio


RealTime/Gutsy (last edited 2008-08-06 16:31:18 by localhost)