Diff for "RealTime" - Ubuntu Wiki

RealTime

Differences between revisions 1 and 114 (spanning 113 versions)

Realtime

Basic introduction is available at:
https://help.ubuntu.com/community/UbuntuStudio/RealTimeKernel

For a more in-depth look at kernels, please see: https://wiki.ubuntu.com/Kernel/Dev

News:
The -preempt and -rt kernels are no longer being developed due to lack of support. Focus has instead turned to the -lowlatency and -realtime kernels, particularly for the the release of Ubuntu 11.04 Natty Narwhal. The long-term goal is to have -lowlatency in the official Ubuntu repositories, while maintaining -realtime in a dedicated PPA.

If you wish to see work continued on -preempt or -rt, you are encouraged to volunteer. To do so, join the Ubuntu Studio Developers e-mail list (see Ubuntu Studio).

Make-up of the team and roles officially assigned:

Kernel Responsibility Matrix
Kernels	Code & Packaging	Upstream Relations	Bug Triage	Kernel/DKMS External Driver Upload	Testing	Video Driver Testing
Lucid -lowlatency i386	none	none	none	none	none	none
Lucid -lowlatency amd64	none	Tim Cook	none	none	Tim Cook	none
Lucid -realtime i386	none	none	none	none	none	Brian David
Lucid -realtime amd64	none	Tim Cook	none	none	Laurent Bellegarde	holstein(nvidia) / Laurent Bellegarde(fglrx)
Natty -lowlatency i386	Luke Yelavich / Scott Lavender / Ronan Jouchet	Scott Lavender	Scott Lavender / Ronan Jouchet	Luke Yelavich	Scott Lavender / Ronan Jouchet	Ronan Jouchet (fglrx), Luke Yelavich (NVIDIA)
Natty -lowlatency amd64	Luke Yelavich	none	none	Luke Yelavich	none	Luke Yelavich (NVIDIA)
Natty -realtime i386	Alessio Igor Bogani	Alessio Igor Bogani	Alessio Igor Bogani	none	none	none
Natty -realtime amd64	Alessio Igor Bogani	Alessio Igor Bogani	Alessio Igor Bogani	none	Tim Cook	holstein(nvidia)

Persons who would want help but not yet assigned to something:
- Asmo Koskinen: Test on -rt on Lucid, Maverick and Natty (AMD64 and i386) with nVidia, M-Audio Delta 66 and Echo Audio Fire 4
- Erik Rasmussen : Test on -rt
- ailo : -rt on Maverick with nvidia
- Brian David: Testing fglrx in all kernel variants, testing -realtime and -rt kernels, if available
- Jeremy Jongepier: Test and packaging on -rt/-realtime
- 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:
Missing a decent FAQ section
Firewire audio devices: again volunteers?

FAQ:
Q: What is the difference between an -rt kernel and a -realtime kernel?

A: From a technical point of view, -rt and -realtime are the same kernel. They are both based on the PREEMPT_RT patchset, although the version may be different. The main difference is that the -rt kernel should be based on the Ubuntu source tree (and therefore can use the same features, patches, enabled hardware, security fixes and so on) and should offer the same services that the Ubuntu default -generic kernel offers. For example, it should be compatible with closed video drivers (nvidia and fglrx), any external DKMS drivers, and have available backport packages. The goal of an -rt kernel is to obtain a real time variant of the Ubuntu kernel that is aligned with the -generic kernel.

On the other hand, the -realtime kernel is a PREEMPT_RT patched kernel based on the vanilla source tree (not the Ubuntu source). This kernel will be missing Ubuntu specific code, patches or security fixes and it isn't guaranteed to be compatible with any external software (low level utilities, DKMS drivers and so on). It does not use the same Linux kernel version as the -generic kernel, and so these two kernels are not aligned. It is a working, upstream real-time kernel that is being used on Ubuntu. No more no less.

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.

RealTime (last edited 2011-02-23 10:51:46 by cache1)

-  ⇤ ← Revision 1 as of 2007-01-09 16:20:53 → 
  Size: 1612
  Editor: adsl203-157-083
  Comment:
+   ← Revision 114 as of 2010-10-12 06:59:28 → ⇥
  Size: 6783
  Editor: cache1
  Comment:
-Deletions are marked like this.
+Additions are marked like this.
 Line 1:
-##(see the SpecSpec for an explanation)
+== Realtime ==
 Line 3:
-''Please check the status of this specification in Launchpad before editing it.  If it is Approved, contact the Assignee or another knowledgeable person before making changes.''
+'''Basic introduction is available at:'''<<BR>>
[[https://help.ubuntu.com/community/UbuntuStudio/RealTimeKernel]]
<<BR>><<BR>>
For a more in-depth look at kernels, please see:
[[https://wiki.ubuntu.com/Kernel/Dev]] <<BR>><<BR>>
'''News:''' <<BR>>
The -preempt and -rt kernels are no longer being developed due to lack of support.  Focus has instead turned to the -lowlatency and -realtime kernels, particularly for the the release of Ubuntu 11.04 Natty Narwhal.  The long-term goal is to have -lowlatency in the official Ubuntu repositories, while maintaining -realtime in a dedicated PPA.<<BR>><<BR>>
If you wish to see work continued on -preempt or -rt, you are encouraged to volunteer.  To do so, join the Ubuntu Studio Developers e-mail list (see [[http://ubuntustudio.org/|Ubuntu Studio]]).
-Line 5:
+Line 12:
-## * '''Launchpad entry''': https://launchpad.net/distros/ubuntu/+spec/realtime
 * '''Created''':  [[Date(2007-01-09T17:28:06Z)]] by AlessioIgorBogani
 * '''Contributors''': AlessioIgorBogani
 * '''Packages affected''': linux-source-2.6.20
+'''Make-up of the team and roles officially assigned:'''
||<-7 #cccccc :> '''Kernel Responsibility Matrix''' ||
||<#eeeeee> '''Kernels''' ||<#eeeeee> '''Code & Packaging''' ||<#eeeeee> '''Upstream Relations''' ||<#eeeeee> '''Bug Triage''' ||<#eeeeee> '''Kernel/DKMS External Driver Upload''' ||<#eeeeee> '''Testing''' ||<#eeeeee> '''Video Driver Testing''' ||
||<#eeeeee> '''Lucid -lowlatency i386''' ||<#FFFFCC> none ||<#FFFFCC> none ||<#FFFFCC> none ||<#FFFFCC> none ||<#FFFFCC> none ||<#FFFFCC> none ||
||<#eeeeee> '''Lucid -lowlatency amd64''' ||<#FFFFCC> none ||<#CCFFCC> Tim Cook ||<#FFFFCC> none ||<#FFFFCC> none ||<#CCFFCC> Tim Cook ||<#FFFFCC> none ||
||<#eeeeee> '''Lucid -realtime i386''' ||<#FFFFCC> none ||<#FFFFCC> none ||<#FFFFCC> none ||<#FFFFCC> none ||<#FFFFCC> none ||<#CCFFCC> Brian David ||
||<#eeeeee> '''Lucid -realtime amd64''' ||<#FFFFCC> none ||<#CCFFCC> Tim Cook ||<#FFFFCC> none ||<#FFFFCC> none ||<#CCFFCC> Laurent Bellegarde ||<#CCFFCC> holstein(nvidia) / Laurent Bellegarde(fglrx) ||
||<#eeeeee> '''Natty -lowlatency i386''' ||<#CCFFCC> Luke Yelavich / Scott Lavender / Ronan Jouchet ||<#CCFFCC> Scott Lavender ||<#CCFFCC> Scott Lavender / Ronan Jouchet ||<#CCFFCC> Luke Yelavich ||<#CCFFCC> Scott Lavender / Ronan Jouchet ||<#CCFFCC> Ronan Jouchet (fglrx), Luke Yelavich (NVIDIA) ||
||<#eeeeee> '''Natty -lowlatency amd64''' ||<#CCFFCC> Luke Yelavich ||<#FFFFCC> none ||<#FFFFCC> none ||<#CCFFCC> Luke Yelavich ||<#FFFFCC> none ||<#CCFFCC> Luke Yelavich (NVIDIA) ||
||<#eeeeee> '''Natty -realtime i386''' ||<#CCFFCC> Alessio Igor Bogani ||<#CCFFCC> Alessio Igor Bogani ||<#CCFFCC> Alessio Igor Bogani ||<#FFFFCC> none ||<#FFFFCC> none ||<#FFFFCC> none ||
||<#eeeeee> '''Natty -realtime amd64''' ||<#CCFFCC> Alessio Igor Bogani ||<#CCFFCC> Alessio Igor Bogani ||<#CCFFCC> Alessio Igor Bogani ||<#FFFFCC> none ||<#CCFFCC> Tim Cook ||<#CCFFCC> holstein(nvidia) ||
-Line 10:
+Line 24:
-== Summary ==
+'''Persons who would want help but not yet assigned to something:''' <<BR>>
- Asmo Koskinen: Test on -rt on Lucid, Maverick and Natty (AMD64 and i386) with nVidia, M-Audio Delta 66 and Echo Audio Fire 4 <<BR>>
- Erik Rasmussen : Test on -rt <<BR>>
- ailo : -rt on Maverick with nvidia <<BR>>
- Brian David: Testing fglrx in all kernel variants, testing -realtime and -rt kernels, if available<<BR>>
- Jeremy Jongepier: Test and packaging on -rt/-realtime <<BR>>
- Janne Jokitalo: Testing, packaging, Ubuntu and Ubuntu Studio relation, learning to generally tweak kernels <<BR>>
-Line 12:
+Line 32:
-This specification details the plan to add hard real time support in Ubuntu.
+'''Work in progress:''' <<BR>>
Nvidia on -realtime kernel at Alessio's PPA: testers? <<BR>>
-Line 14:
+Line 35:
-== Rationale ==
-Line 16:
+Line 36:
-In some contexts (i.e. industrial automation, robotics and telco) the low-latency support is insufficient. In order to push Ubuntu in these contexts is necessary the support for high resolution timers and the full preemption in the Linux kernel. These features have been implemented by Thomas Gleixner and Ingo Molnar (http://people.redhat.com/mingo/realtime-preempt/).
+'''Known issues:''' <<BR>>
Missing a decent FAQ section <<BR>>
Firewire audio devices: again volunteers? <<BR>>
-Line 18:
+Line 40:
-We want also a valid FLOSS alternative to SLERT (http://www.novell.com/products/realtime/).
-Line 20:
+Line 41:
-== Use cases ==
+'''FAQ:''' <<BR>>
Q: What is the difference between an -rt kernel and a -realtime kernel?
-Line 22:
+Line 44:
-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.
+A: From a technical point of view, -rt and -realtime are the same kernel. They are both based on the PREEMPT_RT patchset, although the version may be different. The main difference is that the -rt kernel should be based on the Ubuntu source tree (and therefore can use the same features, patches, enabled hardware, security fixes and so on) and should offer the same services that the Ubuntu default -generic kernel offers. For example, it should be compatible with closed video drivers (nvidia and fglrx), any external DKMS drivers, and have available backport packages. The goal of an -rt kernel is to obtain a real time variant of the Ubuntu kernel that is aligned with the -generic kernel.
<<BR>><<BR>>
On the other hand, the -realtime kernel is a PREEMPT_RT patched kernel based on the vanilla source tree (not the Ubuntu source). This kernel will be missing Ubuntu specific code, patches or security fixes and it isn't guaranteed to be compatible with any external software (low level utilities, DKMS drivers and so on).  It does not use the same Linux kernel version as the -generic kernel, and so these two kernels are not aligned. It is a working, upstream real-time kernel that is being used on Ubuntu.  No more no less.
-Line 24:
+Line 48:
-== Scope ==
+{{{#!wiki comment
-Line 26:
+Line 50:
-This specification cover the linux kernel in Ubuntu.
+-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.
-Line 28:
+Line 55:
-== Design ==
+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.
-Line 30:
+Line 61:
-== Implementation ==
-Line 32:
+Line 62:
-We hope to add a linux-image-realtime package in universe repositary (the same place of the linux-image-lowlatency package).
+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.
-Line 34:
+Line 67:
-=== Code ===
+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).
-Line 36:
+Line 75:
-=== Data preservation and migration ===
+}}}
-Line 38:
+Line 77:
-== Unresolved issues ==
-Line 40:
+Line 78:
-== BoF agenda and discussion ==
+=== Ancient stuff ===
These wiki pages covers hard real time support in Ubuntu.
-Line 42:
+Line 81:
-----
CategorySpec CategorySpec
+[[RealTime/Feisty|RealTime Feisty]] <<BR>>
[[RealTime/Gutsy|RealTime Gutsy]] <<BR>>
[[RealTime/Hardy|RealTime Hardy]] <<BR>>
[[RealTime/Intrepid|RealTime Intrepid]] <<BR>>
[[RealTime/Jaunty|RealTime Jaunty]] <<BR>>
[[RealTime/Karmic|RealTime Karmic]] <<BR>>
[[RealTime/Lucid|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 [[http://rt.wiki.kernel.org|rt.wiki.kernel.org]] and the [[http://ubuntustudio.org/|Ubuntu Studio]] team for more information.