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This specification details the plan to improve hard real time support in Ubuntu Hardy. In particular, to comply with quality levels that users want from an LTS release.


In order to push Ubuntu in very highly demanding business (e.g. industrial automation, financial, robotics, advanced multimedia and telco) and other contexts, it is necessary to improve real-time kernel flavour support.

Use Cases

1. Deterministic (Hard-Realtime) [Industrial Control, Robotics, Automation, DAQ, etc.]

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

  • John is using the Ubuntu distribution, with the linux-rt kernel, as the RTOS, for a GANTRY type widget assembly application. The system has digital I/O, servo motors, and GPIB instrumentation.

2. Non-Deterministic (Low-Latency) [Data Sampling, Analysis Tools, Realtime Monitoring, etc.]

  • Beth is a user wanting application stability but with real-time performance capability for running Audio and MIDI applications (such as JACK and its clients). This could include running a full X/Gtk UI stack with Wine and/or FST, with networking to allow for collaborative performances (e.g. NINJAM). Stability: must be reliable enough for live performance (system hangs look terribly unprofessional). Performance: no dropped MIDI messages (hanging notes suck...), no dropped audio frames (audio glitches suck...).


This specification covers the rt linux kernel flavour in Ubuntu.


We will use the new kernel build system created by the Ubuntu Kernel Team for production kernel: More nformation about it.

Rt-tests packages will be released through Alessio's PPA archive.

We use Git for handle kernel source code and Quilt for handle the preempt-rt one.

Other utilities as like Preemption test or hackbench are postponed to hardy+1. It is the same for integration with PolicyKit (framework for secure privilege elevation integration) and for RT related documentation due to lack of interest.

Outstanding 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 (probably local only)
3. Restricted modules increase latencies (please buy only hardware which have a free driver!)

Packages available

Packages available in Hardy archive:

Packages available in Alessio's PPA archive:


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) We use _only_ the full Ubuntu Kernel (not vanilla, not custom version or other). The Ubuntu Realtime kernel is the Ubuntu Kernel plus the real-time pre-emption patch. Also the configuration (aka /boot/config*) is the same except for specific real-time options.

Q) Where can I find documentation?
A) All existing docs are available on http://rt.wiki.kernel.org

Q) What are the differences from 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/linux-restricted-modules) and also remove all code which isn't strictly related to real-time preemption support (if any).

Q) What features will be included in Ubuntu rt kernel flavour?
A) CPU shielding, priority inheritance, sleeping spinlocks, interrupt threads and high-resolution timers and CFS optimizations.

Q) How to get the source code? Is there a Git repository?
A) Sure! You can find it at Ubuntu Kernel Team's Git Repositories.

Q) Why is SMP disabled
A) See bug report 290498 and its duplicates (Do you know more on this subject? Please write a note here!).

BoF agenda and discussion

  • Any suggestions/feedbacks/requests? Alessio

  • Is it available for i386, amd64 and ppc ?
    • Unfortunately only i386 and amd64 are available so no ppc rt kernel flavour at the moment due to lack of resources (mainly ppc systems!)


RealTime/Hardy (last edited 2008-11-07 15:34:02 by d83-183-69-42)