RealTime
Realtime
Basic introduction is available at:
https://help.ubuntu.com/community/UbuntuStudio/RealTimeKernel
Make-up of the team:
Leader |
|
vacant |
Code & Packaging |
-lowlatency |
Luke Yelavich |
Bug triage |
|
vacant |
Kernel and DKMS external driver upload |
-lowlatency |
Luke Yelavich |
Test |
|
vacant |
Persons who would want help but not yet assigned to something:
- Asmo Koskinen:
- Erik Rasmussen : Test on -rt
- Mike Holstein : -realtime on Lucid
- ailo : -rt on Maverick with nvidia
- Brian David:
- Laurent Bellegarde: testing, advertising, conference, demonstration to large public
- Tim Cook: test on -rt and Relationships with other communities
- Jeremy Jongepier: Test and packaging on -rt/-realtime
- Scott Lavender: testing, packaging, Ubuntu relations, and Studio relation about -lowlatency
- Janne Jokitalo: Testing, packaging, Ubuntu and Ubuntu Studio relation, learning to generally tweak kernels
Work in progress:
Nvidia on -realtime kernel at Alessio's PPA: testers?
Known issues:
ATI (fglrx): volunteers?
Firewire audio devices: again volunteers?
Ancient stuff
These wiki pages covers hard real time support in Ubuntu.
RealTime Feisty
RealTime Gutsy
RealTime Hardy
RealTime Intrepid
RealTime Jaunty
RealTime Karmic
RealTime Lucid
The RT kernel is still around! If you can help by describing it's current state, please do so. In the mean time see the official rt.wiki.kernel.org and the Ubuntu Studio team for more information.
-lowlatency == -generic + more aggressive low latency kernel configuration It can offers all things that Ubuntu offer with -generic so -backport modules, video closed drivers and so on. It is very solid and oriented to "soft" users. Trade-off between low latency and power consumption.
-rt == -generic + plus PREEMPT_RT patchset (this is the realtime Linux) It would want offer the same but require a lot of works. it would want be aligned with -generic version but it can't be able. It isn't very solid and it is oriented to "hard" users only. Power consumption is a secondary concern.
-realtime == vanilla (kernel.org) + plus PREEMPT_RT patchset (this is the realtime Linux) It don't be interested neither to be aligned with -generic kernel nor be compatible with all closed video rivers shipped (and worked) with Ubuntu. It don't provide -backport drivers. it is very stable and it is oriented to "hard" users only. Power consumption is a secondary concern.
From a technical point of view -rt and -realtime are the same kernel. A minor difference is that the -rt kernel offer the "really stable" and upstream official release 2.6.31 whereas -realtime offers the last official upstream release that is 2.6.33. But there are the same kernel (that is PREEMPT_RT). The main difference is the external support. In -rt I have tried to offer an usable system as like Ubuntu do (so I have worked on compatibility with closed video drivers for example like nvidia or fglrx) whereas with -realtime I don't enforce it at all.
In less words: if you need of closed video drivers, external DKMS kernel modules, linux-backports-* you should probably start to use -lowlatency (when it will be available through Ubuntu repos). Instead if you really need of an real-time system you should avoid all above or trying to make those working alone.
To put it simply: -lowlatency all the way! It delivers impressive results for maintenance requirements way lower than -realtime (or -rt even more), meaning less work for maintainers and new kernel candy for users.
Life is a trade-off: someone want a very hard real-time system without adopt other hardware architectures than pc (MCU, FPGA/ASIC, and so on), others want use normal and cheap pc, others want use also accelerated drivers also, others want a real-system which take care of they laptop's batteries too. And at the end we have limited resources(*) for give an answer on these needs (we are all volunteers).