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• Launchpad entry: https://blueprints.launchpad.net/ubuntu/+spec/realtime-hardy

• Created: Date(2007-10-17T14:57:00Z) by AlessioIgorBogani

• Contributors: PeterLJones

• Source Package:

• Binaries Packages:

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

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.

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.

Assumptions

• [wiki:KernelTeam/Hardy/KernelVersion Kernel Version]: 2.6.24?

• [http://lwn.net/Articles/230501/ Scheduler] in stock kernel: CFS

Outstanding Issues

• How will -rt fare with the introduction of CFS, replacing O(1).

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).

BoF agenda and discussion

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

*) 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

*) RT Test suite? BR Thomas Glexiner's rt-tests tools: http://git.kernel.org/?p=linux/kernel/git/tglx/rt-tests.git;a=summary

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

• Any suggestions/feedbacks/requests? [wiki:AlessioIgorBogani Alessio] BRBR

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