The different realtime kernels

[Ralf Mardorf]

On Thu, 2010-09-30 at 13:25 -0500, Scott Lavender wrote:
> 
> On Thu, Sep 30, 2010 at 11:44 AM, Ralf Mardorf
> <ralf.mardorf at alice-dsl.net> wrote:
>         On Thu, 2010-09-30 at 17:15 +0100, Ricardo Lameiro wrote:
>         > I agree with you. I think the best compromise is to use the
>         Hard RT
>         > kernel patch on top of vanilla kernel, and have the Generic
>         kernel for
>         > everyday usage.
>         > You can choose which kernel to boot from at the beginning,
>         
>         
>         I only use vanilla + rt-patched kernels for audio-video and
>         everyday
>         usage. The only difference is the CPU frequency scaling. For
>         everyday
>         usage I set it to ondemand and for audio-video work to
>         performance and
>         sometimes I manually enable hr timer when doing MIDI work.
>         
>         IMO just a kernl-rt is needed, but as I mentioned before,
>         people running
>         32-bit architecture might need a patch to enable usage of
>         large RAM.
>         
>         But indeed, GRUB is our friend, we are free to use several
>         kernels. OT:
>         GRUB is a little bit more user-friendly than GRUB2 is ;).
>         
>         > Hard RT kernel, should be the only one to be supported,
>         since it is
>         > the kernel that brings more benefits to audio/video
>         production, If we
>         > spread attention with 2 more kernel flavours, no one can
>         support it,
>         > and lets face it, abogani makes a hell of a good job, so we
>         should
>         > simplify is life :D
>         
>         
>         Hm, on my Ubuntu Studio, neither Abogani's, anyone else or my
>         own build
>         kernel-rt are ok :(. I can't boot any kernel-rt.
>         
>         I'm able to run Suse with my self build kernel-rt, but not
>         with the
>         repositories once and I'm able to run 64 Studio (Hardy,
>         Karmic) with
>         kernel-rt from the repositories and self build kernels.
>         
>         Live CDs, e.g. AV Linux are ok with the kernel-rt.
>         
>         Anyway, the rt-patch could be a PITA, while the PREEMPT only
>         kernel for
>         Ubuntu Studio is ok on my machine, as far as a PREEMPT only
>         kernel is
>         able to do some jobs, but I'm able to boot the kernel.
>         
>         IMO we only should take care of the kernel-rt and no other
>         kernel.
>         Hard disk drives today are less expensive so everybody should
>         be able to
>         install a distro for audio-video usage and if needed other
>         distros for
>         other usages, because not only the kernel makes a different.
>         IMO a DAW
>         e.g. don't need the security that's needed for some other
>         usages.
>         
>         I'm running several Linux, no Windows, on my 2 core AMD 64-bit
>         PC, for
>         everyday usage and audio-MIDI productions, all Linux with
>         kernel-rt
>         only, excepted Ubuntu Studio, because I didn't had the time to
>         troubleshoot why I'm unable to boot a kernel-rt for Ubuntu
>         Studio.
>         
>         I prefer 64 Studio, but I really like Suse and Ubuntu Studio
>         too, of
>         course there are some other good distros, but those three are
>         my
>         favourites, even if Ubuntu Studio until today isn't ready for
>         production.
>         I like the concept of Ubuntu Studio, excepted of the default
>         PREEMPT
>         kernel, without rt-patch.
>         
>         This are just my personal 2 cents, the advantage of Linux,
>         that we do
>         have a lot of different paths we could go, even if it
>         sometimes seems to
>         be a disadvantage.
>         
>         
>         
>         
>         --
>         
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>         Ubuntu-Studio-users at lists.ubuntu.com
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>         
> 
> This isn't necessarily addressed to Ralf, but it ties in with the
> comments in his email.
> 
> Ubuntu Studio as a project makes far fewer decisions that people
> probably expect.  The kernel is a good example.
> 
> The Ubuntu Studio team did not decide to remove the -rt kernel from
> the ISO image because we think it is inferior or that another kernel
> performs better.  We would like to still be able to provide it to our
> users because we understand that it yields performance that other
> kernels cannot provide.  We can no longer provide the -rt kernel in
> the ISO image because it is no longer in the official archives.
> 
> Ubuntu Studio exists and must maneuver within Canonical/Ubuntu
> ecosphere.  And sometimes decisions are made by Canonical or Ubuntu
> that grossly affect Ubuntu Studio.  Some of those can be mitigated
> (e.g. ubuntustudio-menu vs. ubuntu menu with social integration) and
> others cannot.
> 
> By the way, mitigating such things is a very good reason to keep
> building ISOs instead of just focusing on a Ubuntu Studio PPA.
> 
> Some of the reasoning to remove the -rt kernel is because of a desire
> to keep the kernel versions aligned between Ubuntu and Ubuntu Studio.
> And since the -rt patch is not available for every kernel version
> release, to continuously maintain the alignment would eventually be
> untenable, as witnessed with Lucid.
> 
> Therefore, Ubuntu Studio is progressing to get the -lowlatency kernel
> accepted and promoted to the official archives.  This way we can offer
> it in the ISO image.  This would provide a performance tuned kernel
> that hopefully most of our users will find acceptable
> "out-of-the-box".  Since the -lowlatency kernel results from compiling
> the -generic kernel with different flags (at least my understanding of
> it), it can be easily and continuously maintained in the repositories.
> 
> For those who still require an -rt kernel, we are planning to
> accommodate those persons by offering the -rt kernel in a PPA.
> However, it should be noted that the -rt kernel version will not
> necessarily align with the kernel offered with any particular current
> Ubuntu Studio release.  As mentioned previously, since we cannot
> control which versions will have a -rt patch released, therefore we
> cannot control which versions can be -rt kernels.  And we certainly
> are not going to have Ubuntu as a whole use an older kernel to keep us
> in sync.
> 
> I would not expect the -rt kernel to ever be in the archives again for
> the reasons mentioned above.  This is a secondary effect of developing
> Ubuntu Studio within the Ubuntu framework.  A small detraction, given
> that we can still offer it in a PPA, given the overwhelming sea of
> gains of working within the framework.
> 
> I hope this clears up any misconceptions.
> 
> Cheers,
> ScottL

2 cents:

Of course the rt-patch isn't available for every vanilla kernel version.

But is it wise to have a distro that includes applications like Ardour,
JAMin, JACK etc. without a kernel-rt?

What do you think would be the answer, if somebody has got an issue when
using Ardour and the person ask at the Ardour users mailing list,
posting that the kernel isn't a kernel-rt?

What is Ubuntu Studio for?

I guess we could install a 'normal' Ubuntu and add Ardour, JACK etc., if
Ubuntu Studio don't support a kernel-rt I don't understand what it
should be for?

Supporting real-time applications without a kernel that is patched with
a rt-patch IMO is pointless.

*?*
Ralf