From 0d795930ffa66660bcfa0ea911f56841c2006a04 Mon Sep 17 00:00:00 2001
From: firestar5683 <168790843+firestar5683@users.noreply.github.com>
Date: Thu, 29 Oct 2026 16:58:34 -0500
Subject: [PATCH] Keep the FLM live receiver at normal CPU priority

---
 openpilot/starpilot/flm/steerlearnerd.py      |  2 +-
 .../flm/tests/test_receiver_scheduling.py     | 32 +++++++++++++++++++
 prebuilt.json                                 |  2 +-
 3 files changed, 34 insertions(+), 2 deletions(-)
 create mode 100644 openpilot/starpilot/flm/tests/test_receiver_scheduling.py

diff --git a/openpilot/starpilot/flm/steerlearnerd.py b/openpilot/starpilot/flm/steerlearnerd.py
index 7497c90e0b..3632c6ba2b 100644
--- a/openpilot/starpilot/flm/steerlearnerd.py
+++ b/openpilot/starpilot/flm/steerlearnerd.py
@@ -1020,7 +1020,7 @@ def main():
   try:
     if hasattr(os, 'sched_setscheduler'):
       os.sched_setscheduler(0, os.SCHED_OTHER, os.sched_param(0))
-    os.nice(10)
+    os.setpriority(os.PRIO_PROCESS, 0, 0)
   except OSError:
     # An optional estimator must not inherit realtime scheduling on failure.
     return
diff --git a/openpilot/starpilot/flm/tests/test_receiver_scheduling.py b/openpilot/starpilot/flm/tests/test_receiver_scheduling.py
new file mode 100644
index 0000000000..aa56cb0b00
--- /dev/null
+++ b/openpilot/starpilot/flm/tests/test_receiver_scheduling.py
@@ -0,0 +1,32 @@
+"""The receiver must reach startup at normal priority; numerical guards stay separate."""
+from unittest import mock
+
+import pytest
+
+from openpilot.starpilot.flm import steerlearnerd
+
+
+class ReachedParams(Exception):
+  pass
+
+
+def test_actual_receiver_main_requests_normal_priority_before_reading_params():
+  with mock.patch.object(steerlearnerd.os, 'sched_setscheduler') as scheduler, \
+       mock.patch.object(steerlearnerd.os, 'setpriority') as priority, \
+       mock.patch.object(steerlearnerd.os, 'nice') as nice, \
+       mock.patch.object(steerlearnerd, 'Params', side_effect=ReachedParams):
+    with pytest.raises(ReachedParams):
+      steerlearnerd.main()
+  scheduler.assert_called_once_with(0, steerlearnerd.os.SCHED_OTHER, mock.ANY)
+  priority.assert_called_once_with(steerlearnerd.os.PRIO_PROCESS, 0, 0)
+  nice.assert_not_called()
+
+
+@pytest.mark.parametrize('failed_call', ['sched_setscheduler', 'setpriority'])
+def test_actual_receiver_main_refuses_unqualified_scheduler_startup(failed_call):
+  with mock.patch.object(steerlearnerd.os, 'sched_setscheduler'), \
+       mock.patch.object(steerlearnerd.os, 'setpriority'), \
+       mock.patch.object(steerlearnerd, 'Params') as params:
+    getattr(steerlearnerd.os, failed_call).side_effect = PermissionError('unavailable')
+    assert steerlearnerd.main() is None
+  params.assert_not_called()
diff --git a/prebuilt.json b/prebuilt.json
index 2e0e06521e..054bd5d14f 100644
--- a/prebuilt.json
+++ b/prebuilt.json
@@ -1 +1 @@
-{"protected_inventory_sha256": "bac7d61b5ba9533b8179581ef7b58b9b12726afd6de30981b7bf78b37b1a9e9b", "schema_version": 1}
+{"protected_inventory_sha256": "b15246eb3fd836cb63fa30ffcb9eadb1d9f7004f984a4b6ef20b5de5e7397c8a", "schema_version": 1}