Remove Realtime Kernel Check (#2777)

Author: bjin2364

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
 -----------

controller_manager/src/ros2_control_node.cpp

@@ -76,31 +76,20 @@ int main(int argc, char ** argv)
   std::thread cm_thread(
     [cm, thread_priority, use_sim_time]()
     {
-      if (realtime_tools::has_realtime_kernel())
-      {
-        if (!realtime_tools::configure_sched_fifo(thread_priority))
-        {
-          RCLCPP_WARN(
-            cm->get_logger(),
-            "Could not enable FIFO RT scheduling policy: with error number <%i>(%s). See "
-            "[https://control.ros.org/master/doc/ros2_control/controller_manager/doc/userdoc.html] "
-            "for details on how to enable realtime scheduling.",
-            errno, strerror(errno));
-        }
-        else
-        {
-          RCLCPP_INFO(
-            cm->get_logger(), "Successful set up FIFO RT scheduling policy with priority %i.",
-            thread_priority);
-        }
-      }
-      else
+      if (!realtime_tools::configure_sched_fifo(thread_priority))
       {
         RCLCPP_WARN(
           cm->get_logger(),
-          "No real-time kernel detected on this system. See "
+          "Could not enable FIFO RT scheduling policy: with error number <%i>(%s). See "
           "[https://control.ros.org/master/doc/ros2_control/controller_manager/doc/userdoc.html] "
-          "for details on how to enable realtime scheduling.");
+          "for details on how to enable realtime scheduling.",
+          errno, strerror(errno));
+      }
+      else
+      {
+        RCLCPP_INFO(
+          cm->get_logger(), "Successful set up FIFO RT scheduling policy with priority %i.",
+          thread_priority);
       }
 
       // for calculating sleep time