Hardy

Revision 21 as of 2007-11-30 17:01:35

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Summary

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.

Rationale

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.]BR

  • Alex is developing an application ([http://en.wikipedia.org/wiki/SCADA 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.]BR

  • Beth is a user wanting application stability but with real-time performance capability for running Audio and MIDI applications (such as [http://jackaudio.org/ JACK] and its clients). This could include running a full [http://www.x.org X]/[http://www.gtk.org Gtk] UI stack with [http://www.winehq.com WINE] and/or [http://www.joebutton.co.uk/fst/ FST], with networking to allow for collaborative performances (e.g. [http://ninjam.com 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...).

Scope

This specification covers the rt linux kernel flavour in Ubuntu.

FAQ

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? BR 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? BR A) All existing docs are available on http://rt.wiki.kernel.org

Q) What are the differences from vanilla Ingo Molnar's patch? BR 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 pre-emption support (if any).

Q) What features will be included in Ubuntu rt kernel flavour? BR 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? BR A) (I belive there is no Git repository. The best way is, I guess, get the Ubuntu kernel from the Git repository at http://kernel.ubuntu.com and then apply the patch from Ingo Molnar. Is there a patch package? Alessio, could you please elaborate on this?)

BoF agenda and discussion

*) Team creation? BR Collaboration with instant messaging, chat or mailing list? BR

*) PolicyKit, framework for secure privilege elevation integration, seems which became default in Hardy. Investigate on possible integration. BR

*) Backport of the last upstream code? BR It is necessary define a tool/method to track rt development and thus eventually backport useful bits.

*) Debug packages? BR See at https://blueprints.launchpad.net/ubuntu/+spec/daily-kernel-builds

There are some other test applications on http://rt.wiki.kernel.org that could also be integrated in a future test suite. And, of course, this test suite could be executed daily, integrated in the daily-kernel-builds referred above. wiki:miguel Miguel

In this way you testing realtime performance of the buildd server (the Ubuntu server that compile kernel). Testing is a very useful things but it is necessary find an other way for do it. wiki:AlessioIgorBogani Alessio

*) RT documentation? BR I believe that it would be necessary to have some documentation package, at least for application developers. As a starting point, the documentation in the http://rt.wiki.kernel.org could be used but I think that something for newcomers should also be written (in cooperation with the http://rt.wiki.kernel.org maintainers, of course).

Good suggestion! wiki:AlessioIgorBogani Alessio

Need to review: BR 1. High precision timers don't work on machine which have only PIT as souce clock [http://www.mail-archive.com/linux-rt-users@vger.kernel.org/msg00375.html more info] BR 2. The realtime kernel could expose you to security issuesBR 3. On some machine esd with realtime kernel freeze GNOME (please kill esd and relaunch it after)BR 4. Restricted modules could increase latencies (please buy only hardware which have a free driver!) BR

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