Realtime or Low-Latency Kernels for OpenSUSE 11.4?

kotakotakota · June 29, 2011, 1:01am

Hello,

I have no idea if this is the right place to ask this, but is there a realtime or low-latency kernel in a repository somewhere for OpenSUSE 11.4? I know I can just compile a rt kernel, but that’s a bit tedious and I’d like to avoid it if possible.
Thanks!!

jdmcdaniel3 · June 29, 2011, 2:04am

The kernel repositories are here, but rt is not compiled for openSUSE 11.4. Here is the link to the kernel repositories:

Index of /repositories/Kernel:

I have a bash script file that can compile a kernel obtained from source here:

S.A.K.C. - SUSE Automated Kernel Compiler - Version 2.00 - Page 7

Message #62 has the most recent version of sakc at 2.50.

May I ask what you want to do with an rt kernel and what you think it will really help?

Thank You,

F_Sauce · June 29, 2011, 2:43am

The realtime kernel developement stopped with version 2.6.33 but you could try using the desktop-kernel, it is supposed to perform decent enough. Or, you could compile your own using the source package ‘kernel-source-rt 2.6.33’ or earlier.

This is a nice site to look for tips and howtos for setting up your computer with low latency: start [LinuxMusicians Wiki]

Cheers

kotakotakota · June 29, 2011, 4:03am

Thanks for the quick responses!!

@jdmcdaniel3, I was hoping to play around with some audio synth and the sort; I enjoy poking around in the various fields. It seems though, if what F_Sauce says is true, then I would not need the realtime kernel for that. The other reason is because I build robots, and since Ubuntu is used for some robots (I don’t like Ubuntu very much), why not openSUSE? A realtime kernel tends to help with robotics quite a bit. Of course, compiling openSUSE for the hardware I use is not something I’d like to do, so I think It makes sense to stay with Gentoo for that work.

Again, thank you!

jdmcdaniel3 · June 29, 2011, 4:10am

Thanks for the quick responses!!

@jdmcdaniel3, I was hoping to play around with some audio synth and the sort; I enjoy poking around in the various fields. It seems though, if what F_Sauce says is true, then I would not need the realtime kernel for that. The other reason is because I build robots, and since Ubuntu is used for some robots (I don’t like Ubuntu very much), why not openSUSE? A realtime kernel tends to help with robotics quite a bit. Of course, compiling openSUSE for the hardware I use is not something I’d like to do, so I think It makes sense to stay with Gentoo for that work.

Again, thank you!

I just wonder if with the speed of present hardware such as an i7 CPU and the much faster kernel’s including 2.6.39 and up through 3.0-rc5, if the rt kernel is really needed anymore. Further, with the bash script file sakc, one could mess around with disabling and removing unneeded stuff from the kernel if you wanted to. Since development seemed to stop for kernel-rt and openSUSE, why was that I wonder? Anyway, good luck in your pursuits.

Thank You,

martin_helm · June 29, 2011, 11:44am

jdmcdaniel3 wrote:
> I just wonder if with the speed of present hardware such as an i7 CPU
> and the much faster kernel’s including 2.6.39 and up through 3.0-rc5, if
> the rt kernel is really needed anymore.

I do a little bit of embedded programming myself as a hobby (not as my job).
What I can say is - the question if you need real time or not is not about
speed, but about deterministic timing and behaviour and that you can not get
with a standard kernel even if you throw hardware at it which is 100 or 1000
times faster than an i7.
This is a general thing. RT is about determinism not speed.

jdmcdaniel3 · June 29, 2011, 1:02pm

I do a little bit of embedded programming myself as a hobby (not as my job).
What I can say is - the question if you need real time or not is not about
speed, but about deterministic timing and behaviour and that you can not get
with a standard kernel even if you throw hardware at it which is 100 or 1000
times faster than an i7.
This is a general thing. RT is about determinism not speed.

Perhaps so however, as the kernel-rt source gets older, its not going to be a choice for openSUSE. Any idea why the support for this is no longer there for us?

Thank You,

martin_helm · June 29, 2011, 2:01pm

jdmcdaniel3 wrote:
> Perhaps so however, as the kernel-rt source gets older, its not going
> to be a choice for openSUSE. Any idea why the support for this is no
> longer there for us?
>
Maybe because a RT kernel does not make that much sense in a general purpose
desktop and server linux system, but is a very spezialised use case and
someone who has such a special case has to know enough to compile the kernel
with the appropriate patches. Best starting point here
https://rt.wiki.kernel.org/index.php/Main_Page

In the past I think to remember that it was mainly suser-jengelh who
provided the rt kernels, so it simply needs a new volunteer to build working
rt kernels for openSUSE, which is not trivial since you need also a bunch of
appropriate kernel modules such that a standard hardware does not stop
working and to ensure overall compatibility of the main system with an older
kernel version.

The maintainers of the CONFIG_PREEMPT_RT_Patch are not that many people and
therfore I think can simply not maintain that many versions of the kernel
but a few and that versions then for a long time, also the focus is
obviously not to have always the latest greatest kernel versions suitable
for a new laptop or a new standard PC supported but the hardware which is
used in embedded systems (which also include of course x86 architectures).
If you look at the http://www.kernel.org/pub/linux/kernel/projects/rt/ you
can simply see that patches are available roughly once a year

The use case mentioned by the OP (robots) is something I would not do with a
main stream distro, but with a specialised solution (depends of course on
the robot). Specialised can simply mean strip down the distro to your needs
and compile the kernel yourself, if based on ARM then Debian is a good
choice.

At the end I have of course to add that the multimedia use case of RT and
its benefits is something I have not the simplest clue, that is simply
outside my comfort zone and beyond my knowledge.

kotakotakota · June 29, 2011, 2:36pm

@martin_helm, yes, I agree, as I mentioned before, Gentoo is the usual option we use, although we have used other specialized embedded Linux operating systems. However, it seems that Ubuntu is becoming more and more popular in the robotics world, so it would be interesting to be able to play with openSUSE controlled robots.

I think I read something about Ubuntu’s rt kernel developer quitting… Part of the problem I suspect is that (as usual with OSS) we have too many people trying to make their own versions of the same thing.

F_Sauce · June 29, 2011, 2:44pm

If I remember correctly much of the features provided by the rt-patch and settings which were enabled in the rt-kernel should be incorporated and enabled in the mainstream kernel now, though not the complete preemption feature. I haven’t followed closely but there has been a lot of talk about the 2.6.39 version on LAU mailinglist. This kernel is supposed to be an improvement low-latency wise comparing to the preceding one.

Some info here: https://www.osadl.org/Realtime-Linux.projects-realtime-linux.0.html

martin_helm · June 29, 2011, 2:59pm

Aha, I see in 11.3 it was indeed in the standard repositories (kernel-
rt-2.6.31-6.1). Maybe worth a request in openfate to have it again for the
multimedia people?