ui: lower priority background threads (#38031)

* drop realtime so preempt can happen during swap

* prime state and firehose

* and params

* above

common/realtime.py

@@ -28,6 +28,11 @@ class Priority:
   CTRL_HIGH = 53
 
 
+def drop_realtime() -> None:
+  if sys.platform == 'linux' and not PC:
+    os.sched_setscheduler(0, os.SCHED_OTHER, os.sched_param(0))
+
+
 def set_core_affinity(cores: list[int]) -> None:
   if sys.platform == 'linux' and not PC:
     os.sched_setaffinity(0, cores)

selfdrive/ui/lib/prime_state.py

@@ -6,6 +6,7 @@ import time
 
 from openpilot.common.api import api_get
 from openpilot.common.params import Params
+from openpilot.common.realtime import drop_realtime
 from openpilot.common.swaglog import cloudlog
 from openpilot.system.athena.registration import UNREGISTERED_DONGLE_ID
 from openpilot.selfdrive.ui.lib.api_helpers import get_token
@@ -69,6 +70,7 @@ class PrimeState:
         cloudlog.info(f"Prime type updated to {prime_type}")
 
   def _worker_thread(self) -> None:
+    drop_realtime()
     from openpilot.selfdrive.ui.ui_state import ui_state, device
     while self._running:
       if not ui_state.started and device._awake:

selfdrive/ui/mici/layouts/settings/firehose.py

@@ -5,6 +5,7 @@ import pyray as rl
 
 from openpilot.common.api import api_get
 from openpilot.common.params import Params
+from openpilot.common.realtime import drop_realtime
 from openpilot.common.swaglog import cloudlog
 from openpilot.selfdrive.ui.lib.api_helpers import get_token
 from openpilot.selfdrive.ui.ui_state import ui_state, device
@@ -212,6 +213,7 @@ class FirehoseLayoutBase(Widget):
       cloudlog.error(f"Failed to fetch firehose stats: {e}")
 
   def _update_loop(self):
+    drop_realtime()
     while self._running:
       if not ui_state.started and device._awake:
         self._fetch_firehose_stats()

selfdrive/ui/ui_state.py

@@ -7,6 +7,7 @@ from enum import Enum
 from cereal import messaging, car, log
 from openpilot.common.filter_simple import FirstOrderFilter
 from openpilot.common.params import Params
+from openpilot.common.realtime import drop_realtime
 from openpilot.common.swaglog import cloudlog
 from openpilot.selfdrive.ui.lib.prime_state import PrimeState
 from openpilot.system.ui.lib.application import gui_app
@@ -122,6 +123,7 @@ class UIState:
     device.update()
 
   def _params_refresh_worker(self):
+    drop_realtime()
     while True:
       self.update_params()
       time.sleep(PARAM_UPDATE_TIME)
@@ -256,6 +258,7 @@ class Device:
       self._brightness_thread.start()
 
   def _brightness_worker(self):
+    drop_realtime()
     while True:
       self._brightness_event.wait()
       self._brightness_event.clear()