The different realtime kernels

[Ralf Mardorf]

On Thu, 2010-09-30 at 14:10 -0500, Scott Lavender wrote:

> [snip]
> This is not a rhetorical question.  I, as Ubuntu Studio project lead,
> would like to include it.  If you can provide a tenable method to
> include the -rt kernel in the Ubuntu Studio ISO image I would like to
> implement it.
> [snip]

Hi Scott :)

I'm not sure, if I do understand the problem.

Does Ubuntu need the same vanilla kernel version for different kind of
kernels, e.g. to provide packages for proprietary graphic modules?
If so, IMO it's not needed to make the multimedia distro full compatible
with a regular Ubuntu.

Multimedia producer just need a kernel-rt and a package including the
headers to compile e.g. drivers for graphics.

For my needs the kernel-rt doesn't provide hard enough real-time, but
the kernel-rt is a compromise that might enable some audio productions.

You might wish to compare a C64, Atari ST or stand alone sequencer from
the eighties with a kernel-rt and a kernel without rt-patch used by a
good classical or jazz musician. There still is too much jitter, but the
kernel-rt for sure will be the first kernel, that might be able to get
the knack of it.

The kernel-rt is the best we do have for Linux, hence it's invalid to
use a less good kernel, as long as even the kernel-rt isn't able to do
hard real-time.

So, if there should be a rule for Ubuntu, that all patched kernels has
to base on the same vanilla version, which is a good thought, it's not
good for multimedia productions.

The need for hard real-time is an exceptional case, not only for
multimedia production, there are other real-time patches, e.g. for the
Enhanced Machine Controller project.
Some people and you might be fine with a non-real-time patched kernel,
but most professional studios aren't even fine with the kernel-rt or on
Windows  ASIO, resp. ASIO + Nuendo on some machines should be near to
eighties hard real-time.

There are coders who program the rt-patch, to make Linux better and
better, it's not smart if a multimedia distro tries to be smarter by not
using a kernel-rt, because it shouldn't be needed.

The kernel-rt is needed and there should be no rule not to use it.

Btw. to make the issue harder. It's not only that there isn't a rt-patch
for every vanilla kernel, sometimes a current
rt-patch-kernel-combination can be bad, so that we need to keep older
rt-patched kernels. Sometimes it's not possible to keep 'things' that
are available by a generic kernel of the same vanilla version, when
using the rt-patch, but there's no need to keep all kernel features for
real-time audio productions.

Cheers!

Ralf