[PlanetCCRMA] jack_capture with jack 1.9.4 complains about nice value of "-10", wants "-20"

[Kjetil S. Matheussen]

Niels Mayer:
>
> However, for jack_capture-0.9.40-1.fc12.x86_64 wants a nice value of "-20"
> but only gets "-10" .
>
> Is this behavior in jack_capture a hold-over from Jack 1.0 days, and a
> potential incompatibility for jack2?
> [I'm using jack-audio-connection-kit-1.9.4-1.fc12.ccrma.x86_64  with
> "@jackuser - nice -10"]
> ...............
> coggie-161-~> jack_capture
> Recording to "jack_capture_01.wav". Press <Return> or <Ctrl-C> to stop.
> Warning. Could not set priority to -20, only -10.
> You probably have wrong nice value in /etc/security/limits.conf.

There are two processes in jack_capture which are a little bit
more important than normal processes such as GUI processes etc.

One of them is the process which writes to disk. This process
only gets a higher nice value in case more than half of the buffer
is used, which should normally never happen.

The other process is a process which monitors the amount of
buffer which is used. In case the amount of free buffer is at any
time lower than the initial amount (default is 4 seconds), a
little bit more memory (two blocks) is allocated automatically
and added to the buffer.

And it is this second process which is responsible for printing that
warning.

This process is probably not so important that it should run
with the lowest realtime priority, because that's the priority
processes such as midi event handlers use, and allocating memory
using the lowest realtime priority could prevent tasks such as
midi event handlers to respond fast enough.

Instead, it tries to run with the highest normal priority, i.e.
the lowest nice value, since it is a very important task, much
more important than perhaps all other tasks not running realtime. 
And it is also a very lightweight process, so it should not
cause the GUI to stutter for instance.

However, for some reason, fedora only allows normal processes
to set nice value to -10! That doesn't make very much sense
if you are allowed to set processes to run with a realtime
priority. So that's the reason for the warning. The solution
to get rid of the warning is to fix the /etc/security/limits.conf
file.