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Old 04-03-2011, 06:44 AM
Victor henri
 
Default rt kernel

Hello

> Hi Scott,
> I did the same. Bad news: rt isn't for Ubuntu 10.10.
> Bye.
>
>
> 2011/4/2 Scott Bohon >
> I am a newbie to Ubuntu and Linux. I upgraded from Ubuntu 10.10 to
> Studio, but I got a message during the upgrade that essentially said
> linux-rt could not be found. Is linux-rt loaded with the audio package?
> Do I need -rt? How do I check if -rt is loaded? If I still need it, how
> do I get it?
>
> Thank you for your help!
>
> Scott Bohon
> cellist and new techno-musician!
>
>
> you can use a kernel from abogani's PPA... check out
> http://jackschnippes.freeunix.net/index.php/2010/11/04/lowlatency-kernel-and-realtime-kernel-for-ubuntu-10-10-maverick
> ...ALSO, the -generic kernel is quite a bit more appropriate for
> realtime audio these days,

It seems that the -generic kernel in Ubuntu 10.10 (and 11.04) is not very appropriate for that, since the RT_GROUP_SCHED option in the kernel is enabled; it means that it overrides everything that may have been configured in the limits.conf. See jackd FAQ :* http://jackaudio.org/linux_group_sched
This seems specific to Ubuntu (according to Jackd FAQ); so it's probably worth to have a try, but you shouldn't be surprised if you have a lot of Xruns. Then you should considerr other options (see below)

*so just try it, and IF you need lower
> latency for softsynths, or realtime effects proecessing, or if you are
> getting a bunch of xruns, move on to an -rt kernel... also, you can go
> ahead and install 11.04 if you'd like... OR use 10.04 like i am...
> enjoy...

Indeed, there is no RT kernel for Maverick in Alessio Abogani's ppa; however, i've used succesfully the RT kernel for Lucid on my Maverick; it worked fine and it is probably the simplest; another option is to compile to RT kernel yourself (wich takes some time but it not so difficult); i have this doc :

http://www.linuxmao.org/tikiwiki/tiki-index.php?page=compiler+un+noyau+2.6RT

Sorry this is in French, but it is quite understandable, I think; the interesting part is at the very bottom under the title :

Exemple : installation d'un noyau temps réel 2.6.33.7-rt29 sur Ubuntu 10.10

If you want to do it and if you have troubles, I'll be glad to help.

Another option is to wait for Natty Narwal release : in Abogani's ppa, there is a preemt kernel (which should probably be enough) for Natty available...


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>
>
>
> --
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>

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Old 04-03-2011, 10:54 AM
ailo
 
Default rt kernel

On 04/03/2011 08:44 AM, Victor henri wrote:
> It seems that the -generic kernel in Ubuntu 10.10 (and 11.04) is not very appropriate for that, since the RT_GROUP_SCHED option in the kernel is enabled; it means that it overrides everything that may have been configured in the limits.conf. See jackd FAQ : http://jackaudio.org/linux_group_sched
> This seems specific to Ubuntu (according to Jackd FAQ); so it's probably worth to have a try, but you shouldn't be surprised if you have a lot of Xruns. Then you should considerr other options (see below)
>

The cgroups thing is no longer an issue. The information on Jacks page
is no longer up to date. We should ask them to remove that part from
their FAQ.

10.10 was never affected. On 11.04 kernel version 2.6.37 was not usable
without having to recompile it, but the kernel in Natty is now 2.6.38,
which includes a patch that removes this problem.

The performance on 2.6.38 has been going up and down during the
development of Natty. At the moment, it is not bad, though not perfectly
reliable.
Alessio Boganis PPA includes a -lowlatency kernel for Natty, which
performs virtually as well as a -realtime kernel would, for *most* people.

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Old 04-03-2011, 12:15 PM
Victor henri
 
Default rt kernel

Hello

>
> On 04/03/2011 08:44 AM, Victor henri wrote:
> > It seems that the -generic kernel in Ubuntu 10.10 (and 11.04) is not very appropriate for that, since the RT_GROUP_SCHED option in the kernel is enabled; it means that it overrides everything that may have been configured in the limits.conf. See jackd FAQ : http://jackaudio.org/linux_group_sched
> > This seems specific to Ubuntu (according to Jackd FAQ); so it's probably worth to have a try, but you shouldn't be surprised if you have a lot of Xruns. Then you should considerr other options (see below)
> >
>
> The cgroups thing is no longer an issue. The information on Jacks page
> is no longer up to date. We should ask them to remove that part from
> their FAQ.
>
> 10.10 was never affected.

But when I 'sudo make menuconfig' in the /usr/src/linux-headers-2.6.35-22-generic directory (or the -28-generic) the RT_GROUP_SCHED option is enabled...

*On 11.04 kernel version 2.6.37 was not usable
> without having to recompile it, but the kernel in Natty is now 2.6.38,
> which includes a patch that removes this problem.

Is a patch needed for that? Is it not enough to disable the RT_GROUP_SCHED option then compile or recompile?

>
> The performance on 2.6.38 has been going up and down during the
> development of Natty. At the moment, it is not bad, though not perfectly
> reliable.
> Alessio Boganis PPA includes a -lowlatency kernel for Natty, which
> performs virtually as well as a -realtime kernel would, for *most* people.

Yes indeed, I've noticed that; It was such a big and nice surprise to see that a 2.6.37 or 2.6.38 preempt could do almost the same job as a realtime kernel (at least for what I do)
>
> --
> ailo
>

Victor



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Old 04-03-2011, 12:42 PM
ailo
 
Default rt kernel

On 04/03/2011 02:15 PM, Victor henri wrote:
> On 11.04 kernel version 2.6.37 was not usable
>> without having to recompile it, but the kernel in Natty is now 2.6.38,
>> which includes a patch that removes this problem.
>
> Is a patch needed for that? Is it not enough to disable the RT_GROUP_SCHED option then compile or recompile?

I have to admit to not knowing much about the cgroup problem, but at
least it is not affecting the ability to use realtime privilege with the
-generic kernel at this point.
To my knowledge, this is because of a patch included in the 2.6.38
kernel.


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Old 04-03-2011, 07:42 PM
Scott Lavender
 
Default rt kernel

On Sat, Apr 2, 2011 at 9:21 PM, Scott Bohon <scott.bohon@gmail.com> wrote:

I am a newbie to Ubuntu and Linux. I upgraded from Ubuntu 10.10 to

Studio, but I got a message during the upgrade that essentially said

linux-rt could not be found. Is linux-rt loaded with the audio package?

Do I need -rt? How do I check if -rt is loaded? If I still need it, how

do I get it?



Thank you for your help!



Scott Bohon

cellist and new techno-musician!









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Hi Scott,


A lot of the other posts in this thread are pretty intensive and involved, and since you are a professed "newbie" I thought I would add some more explanation.

In this context, the package name "linux-rt" refers to a special type of kernel, the "real-time" kernel.* The "real-time" kernel can help with recording audio because it affords users to experience more stable performance at lower latencies (the amount of time from when a sound is made to when it is heard).


And keep in mind there are two types of considerations, the "stable performance" and "lower latencies" in what I mentioned.* By "stable performance" I mean the avoidance of xruns, which are skips or ugly digital artefacts in recorded audio due to overruns or underruns in the audio buffer.* And "lower latencies" mean that the sound is routed with due consideration so that the sound made is recorded in a timely manner.


Obviously, it doesn't do much good to set the latency extremely low but have many xruns so that the sound recorded has unwanted noise introduced in it.* Conversely, it doesn't do much good to avoid xruns but have a latency so high that it appears that you are playing against your own echo in the Grand Canyon, which throws off timing.


Again, while the linux-generic kernel provides a moderate amount of performance, it is expected that the linux-rt kernel can provide a better performance.* But this also considers in other factors such as your computer and your audio interface.


Lower powered computers (say a netbook) or a USB2 audio interface would provide a lower baseline performance in contrast with a quad-core, 6 gigs of memory desktop machine with an M-Audio Delta 66 PCI card audio interface.


It seems to resolve to a matter of compromise which what you have (hardware) and what you can get (stable performance and latencies).

It would seem that the -rt kernel is a very important thing.* And it is.* Unfortunately it isn't always available.


The linux kernel, in general, is used by everyone and therefore sees much attention.* In contrast, the real-time kernel (which is made by applying a patch to the -generic kernel) is only used by a very niche group and is supported by only a very small group.* In times past, the patch was made and maintained by a single person.* I think the group now consists of three people, but I cannot say how involved each is.* I'm probably wrong on the quantity, though.


But the result of this is that the real-time patch that is created by a very small group of people that provides functionality to a niche group (but very small percentage) of users is not available for every kernel release.* Therefore, we cannot have a real-time kernel for every kernel version released. Unfortunately, this also means that the kernel version chosen for Ubuntu (and therefore Ubuntu Studio) may not align with the available current real-time patch and Ubuntu (and Ubuntu Studio) will not have a real-time kernel for that release.


I think this was a consideration, among with others, that caused the linux-rt kernel to be pulled out of the repositories.* Well, this isn't the most accurate description.* The linux-rt package was kept in the repositories for the extant releases but new linux-rt packages would not be created for future release of Ubuntu.* I think Lucid (10.04) is the last Ubuntu (and Ubuntu Studio) release that had the linux-rt package available from the official repositories.


So, having said all that, to answer your questions:

No the linux-rt package is not loaded with the audio package.* it is a separate package that contains the "real-time" kernel, but is not available for Ubuntu (or Ubuntu Studio) 10.10 from the official repository.


You may need the linux-rt package if you have tried the -generic kernel, adjusted your settings for jack, and still find that you have unacceptable performance.* Likewise, if you have a firewire device you may be suffering from irq conflicts and may need the linux-rt kernel to help you resolve those conflicts.* But again, it all matters as to what hardware you have and what your current performance is.* Without more specifics I doubt anyone can say with certainly whether you need it or not.* But it can help in some cases.


To check if it is loaded, you can start a terminal and type 'uname -a' and enter.* This will give you a description of your currently running kernel.* This is different than going into synaptic and seeing which kernels are available on your computer, this will give you the kernel that is currently running.* For example:

scott@lucid-studio:~$ uname -a
Linux lucid-studio 2.6.33-29-realtime #1-Ubuntu SMP PREEMPT RT Wed Aug 4 17:22:37 UTC 2010 x86_64 GNU/Linux

I am running the "real-time" kernel currently.

If you find that you cannot achieve acceptable performance and you wish to try the real-time kernel on Ubuntu 10.10 or later releases you will most likely need to use an individual's personal package archive, colloquially known as a PPA.* This are like the official repositories for software but are "maintained" by individuals.* I say maintained because you neither know the quality of their work nor how well they keep up with it.* I would stick with ones that many people recommend.* I think someone recommended Falktx's PPA, I would recommend his too.* As to the mechanics of PPA's, rather than assume you need this information and post it, I will wait until you identify that you need the real-time kernel and also that you need to understand how PPA's work.


I hope this expansive email helps you.

If anyone notices where I misspoke or was simply wrong, please do not hesitate to correct me.* I imagine it will help Scott and others greatly to avoid misinformation.


ScottL


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Old 04-03-2011, 09:09 PM
Gerhard Lang
 
Default rt kernel

On my maverick partition I did not see essential benefits against lucid,
so I did an early distupgrade to natty. The actual kernel
2.6.38-7-generic gives me good audioperformance for live softsynths,
live effects, wineasio/reaper, ardour multitrack recording on firewire,
pci alsa and usb-midi, in no way inferior to realtime 2.6.31 and .33
kernels, good buffersize/xrun ratio. For tedious audio work on standard
hardware I see no more need for -rt kernels. I guess there might be a
little profit for audio performance by compiling actual kernel cgroups
disabled, no tics disabled, preemptible kernel enabled and timer
frequency set to 1000hz. In future optional manipulating devices' IRQ
assignment and priorities like this was done by rtirq should be a
feature for standard kernels.

best regards
Gerhard

Am 03.04.2011 04:21, schrieb Scott Bohon:

I am a newbie to Ubuntu and Linux. I upgraded from Ubuntu 10.10 to
Studio, but I got a message during the upgrade that essentially said
linux-rt could not be found. Is linux-rt loaded with the audio package?
Do I need -rt? How do I check if -rt is loaded? If I still need it, how
do I get it?

Thank you for your help!

Scott Bohon
cellist and new techno-musician!






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Old 04-04-2011, 12:51 PM
Alessio Igor Bogani
 
Default rt kernel

Hi,

2011/4/3 Gerhard Lang <lang.gerhard@gmail.com>:
[...]
> buffersize/xrun ratio. For tedious audio work on standard hardware I see no
> more need for -rt kernels.

I would be very happy if we could live without -rt kernel.

> I guess there might be a little profit for audio
> performance by compiling actual kernel cgroups disabled, no tics disabled,
> preemptible kernel enabled and *timer frequency set to 1000hz.

This is exactly the -lowlatency kernel.

> optional manipulating devices' IRQ assignment and priorities like this was
> done by rtirq should be a feature for standard kernels.

I hope to provide soon a new -lowlatency kernel which provide that
feature (which is available in 2.6.39).

Ciao,
Alessio

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Old 04-04-2011, 04:34 PM
Victor henri
 
Default rt kernel

Hello

I compile myself the preempt kernel usually.


> 2011/4/3 Gerhard Lang <lang.gerhard@gmail.com>:
> [...]
> > buffersize/xrun ratio. For tedious audio work on standard hardware I see no
> > more need for -rt kernels.
>
> I would be very happy if we could live without -rt kernel.
>
> > I guess there might be a little profit for audio
> > performance by compiling actual kernel cgroups disabled, no tics disabled,
> > preemptible kernel enabled and *timer frequency set to 1000hz.
>

For the preemptible kernel, I was aware of the "preemptible kernel" and "timer frequency = 1000Hz" options;

Could please tell for the @ other otptions:
*** - for the cgroups disabled: is it the "General Setup -> Control Group Support" set to 'no'?
*** - for the "no tics" options disabled, is is the "Processor Type and Features -> High Resolution Timer Support" set to 'no'? If not, what is the option to be disabled?

> This is exactly the -lowlatency kernel.
>
> > optional manipulating devices' IRQ assignment and priorities like this was
> > done by rtirq should be a feature for standard kernels.
>
> I hope to provide soon a new -lowlatency kernel which provide that
> feature (which is available in 2.6.39).
>
> Ciao,
> Alessio
>

Thank you

Victor

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Old 04-05-2011, 06:32 AM
Alessio Igor Bogani
 
Default rt kernel

Victor,

2011/4/4 Victor henri <nadaeck@hotmail.com>:
[...]
> *** - for the cgroups disabled: is it the "General Setup -> Control Group Support" set to 'no'?

No need to disable cgroup anymore.

> *** - for the "no tics" options disabled, is is the "Processor Type and Features -> High Resolution Timer Support" set to 'no'? If not, what is the option to be disabled?

# CONFIG_NO_HZ is not set

Ciao,
Alessio

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Old 04-05-2011, 11:08 AM
Victor henri
 
Default rt kernel

> Victor,
>
> 2011/4/4 Victor henri :
> [...]
> > - for the cgroups disabled: is it the "General Setup -> Control Group Support" set to 'no'?
>
> No need to disable cgroup anymore.
>
> > - for the "no tics" options disabled, is is the "Processor Type and Features -> High Resolution Timer Support" set to 'no'? If not, what is the option to be disabled?
>
> # CONFIG_NO_HZ is not set
>
> Ciao,
> Alessio

Thank you so much Alessio

Victor

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