The different realtime kernels
jeremy at autostatic.com
Thu Sep 30 20:13:53 BST 2010
On 09/30/2010 08:40 PM, Ralf Mardorf wrote:
> 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
>> usage. The only difference is the CPU frequency scaling. For
>> 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
>> > 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
>> 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
>> 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
>> only, excepted Ubuntu Studio, because I didn't had the time to
>> troubleshoot why I'm unable to boot a kernel-rt for Ubuntu
>> 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
>> favourites, even if Ubuntu Studio until today isn't ready for
>> I like the concept of Ubuntu Studio, excepted of the default
>> 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.
>> Ubuntu-Studio-users mailing list
>> 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.
> 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.
It's not pointless.
A lot of stuff from the patch-set has been integrated in the vanilla
kernel already throughout the years. It is perfectly possible to run an
audio production PC without a real-time kernel these days.
I wouldn't need a real-time kernel if the FireWire controller in my
notebook for instance would sit on its own IRQ. But no, it shares its
IRQ with a dozen of other devices so I really need a real-time kernel to
prioritize my FireWire IRQ thread. If it wasn't for that I would be
perfectly happy with -lowlatency.
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