Realtime shield (#2194)

* cpu 3 shield

* set priority before affinity

* add to release files

* only run on android

RELEASES.md

@@ -1,6 +1,7 @@
 Version 0.7.9 (2020-XX-XX)
 ========================
  * Improved car battery power management
+ * Improved realtime performance
 
 Version 0.7.8 (2020-08-19)
 ========================

common/realtime.py

@@ -33,8 +33,8 @@ def set_core_affinity(core):
 
 def config_rt_process(core, priority):
   gc.disable()
-  set_core_affinity(core)
   set_realtime_priority(priority)
+  set_core_affinity(core)
 
 
 class Ratekeeper():

release/files_common

@@ -80,6 +80,7 @@ selfdrive/logmessaged.py
 selfdrive/tombstoned.py
 selfdrive/pandad.py
 selfdrive/updated.py
+selfdrive/rtshield.py
 
 selfdrive/athena/__init__.py
 selfdrive/athena/athenad.py

selfdrive/manager.py

@@ -188,6 +188,7 @@ managed_processes = {
   "updated": "selfdrive.updated",
   "dmonitoringmodeld": ("selfdrive/modeld", ["./dmonitoringmodeld"]),
   "modeld": ("selfdrive/modeld", ["./modeld"]),
+  "rtshield": "selfdrive.rtshield",
 }
 
 daemon_processes = {
@@ -227,6 +228,7 @@ if not PC:
 if ANDROID:
   persistent_processes += [
     'updated',
+    'rtshield',
   ]
 
 car_started_processes = [

selfdrive/rtshield.py

@@ -0,0 +1,16 @@
+#!/usr/bin/env python3
+import time
+from common.realtime import set_core_affinity, set_realtime_priority
+
+
+# RT shield - ensure CPU 3 always remains available for RT processes
+#   runs as SCHED_FIFO with minimum priority to ensure kthreads don't
+#   get scheduled onto CPU 3, but it's always preemptible by realtime
+#   openpilot processes
+
+def main():
+  set_core_affinity(3)
+  set_realtime_priority(1)
+
+  while True:
+    time.sleep(0.000001)