Try using SCHED_FIFO on any kernel (#1142)

(cherry picked from commit 0a3705f)

Author: fmauch

controller_manager/doc/userdoc.rst

@@ -11,10 +11,9 @@ Determinism
 -----------
 
 For best performance when controlling hardware you want the controller manager to have as little jitter as possible in the main control loop.
-The normal linux kernel is optimized for computational throughput and therefore is not well suited for hardware control.
-The two easiest kernel options are the `Real-time Ubuntu 22.04 LTS Beta <https://ubuntu.com/blog/real-time-ubuntu-released>`_ or `linux-image-rt-amd64 <https://packages.debian.org/bullseye/linux-image-rt-amd64>`_ on Debian Bullseye.
 
-If you have a realtime kernel installed, the main thread of Controller Manager attempts to configure ``SCHED_FIFO`` with a priority of ``50``.
+Independent of the kernel installed, the main thread of Controller Manager attempts to
+configure ``SCHED_FIFO`` with a priority of ``50``.
 By default, the user does not have permission to set such a high priority.
 To give the user such permissions, add a group named realtime and add the user controlling your robot to this group:
 
@@ -36,6 +35,15 @@ Afterwards, add the following limits to the realtime group in ``/etc/security/li
 
 The limits will be applied after you log out and in again.
 
+The normal linux kernel is optimized for computational throughput and therefore is not well suited for hardware control.
+Alternatives to the standard kernel include
+
+- `Real-time Ubuntu 22.04 LTS Beta <https://ubuntu.com/blog/real-time-ubuntu-released>`_ on Ubuntu 22.04
+- `linux-image-rt-amd64 <https://packages.debian.org/bullseye/linux-image-rt-amd64>`_ on Debian Bullseye
+- lowlatency kernel (``sudo apt install linux-lowlatency``) on any ubuntu
+
+Though installing a realtime-kernel will definitely get the best results when it comes to low
+jitter, using a lowlatency kernel can improve things a lot with being really easy to install.
 
 Subscribers
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