Real-time fixes (#2630)

* Fix path of cpu.rt_runtime_us sysfs file

Fix detection of CPU bandwidth allocation (CONFIG_RT_GROUP_SCHED) option
by checking the correct file location.

* Set priority limit and memory lock limit

Set a soft limit of real-time priority 90 and hard limit of 99. The
maximum is 99, to avoid add-ons using such a high priority without
second thought set the soft limit to 90. This allows a process to higher
the limit to 99, if really required.

Also set max locked memory to 128MB. Locking memory from getting paged
out is often used for the real-time process/thread to avoid delays due
to swapping/pageing in. Ideally a real-time process should only do the
real-time job, hence not need too much memory.

* Remove check for support_cpu_realtime and set correct limit for audio plug-in

supervisor/docker/__init__.py

@@ -61,7 +61,7 @@ class DockerInfo:
     @property
     def support_cpu_realtime(self) -> bool:
         """Return true, if CONFIG_RT_GROUP_SCHED is loaded."""
-        if not Path("/sys/fs/cgroup/cpu.rt_runtime_us").exists():
+        if not Path("/sys/fs/cgroup/cpu/cpu.rt_runtime_us").exists():
             return False
         return bool(os.environ.get(ENV_SUPERVISOR_CPU_RT, 0))
 

supervisor/docker/addon.py

@@ -265,8 +265,12 @@ class DockerAddon(DockerInterface):
         limits: List[docker.types.Ulimit] = []
 
         # Need schedule functions
-        if self.addon.with_realtime and self.sys_docker.info.support_cpu_realtime:
-            limits.append(docker.types.Ulimit(name="rtprio", soft=99))
+        if self.addon.with_realtime:
+            limits.append(docker.types.Ulimit(name="rtprio", soft=90, hard=99))
+
+            # Set available memory for memlock to 128MB
+            mem = 128 * 1024 * 1024
+            limits.append(docker.types.Ulimit(name="memlock", soft=mem, hard=mem))
 
         # Return None if no capabilities is present
         if limits:

supervisor/docker/audio.py

@@ -59,9 +59,8 @@ class DockerAudio(DockerInterface, CoreSysAttributes):
     @property
     def ulimits(self) -> List[docker.types.Ulimit]:
         """Generate ulimits for audio."""
-        if not self.sys_docker.info.support_cpu_realtime:
-            return None
-        return [docker.types.Ulimit(name="rtprio", soft=99)]
+        # Pulseaudio by default tries to use real-time scheduling with priority of 5.
+        return [docker.types.Ulimit(name="rtprio", soft=10, hard=10)]
 
     @property
     def cpu_rt_runtime(self) -> Optional[int]: