[thermalctld] Use interval set in thermal policy if available (#164)

Description
Update thermalctld to retrieve interval from thermal manager (which in turn loads an interval from thermal_policy.json) instead of using a constant.

Motivation and Context
sonic-net/sonic-platform-common#178

This will allow platform vendors to specify an alternate interval for running thermal policies, e.g. 15 seconds instead of the current 60.

How Has This Been Tested?
Verified that thermalctld runs without exiting.
Also ran test_thermalctld.py

sonic-thermalctld/scripts/thermalctld

@@ -774,6 +774,8 @@ class ThermalControlDaemon(daemon_base.DaemonBase):
                 self.thermal_manager.initialize()
                 self.thermal_manager.load(ThermalControlDaemon.POLICY_FILE)
                 self.thermal_manager.init_thermal_algorithm(self.chassis)
+                # Use thermal manager interval if it's available
+                self.wait_time = self.thermal_manager.get_interval()
         except NotImplementedError:
             self.log_warning('Thermal manager is not supported on this platform')
         except Exception as e:
@@ -832,9 +834,10 @@ class ThermalControlDaemon(daemon_base.DaemonBase):
         except Exception as e:
             self.log_error('Caught exception while running thermal policy - {}'.format(repr(e)))
 
+        interval = self.thermal_manager.get_interval() if self.thermal_manager else self.INTERVAL
         elapsed = time.time() - begin
-        if elapsed < self.INTERVAL:
-            self.wait_time = self.INTERVAL - elapsed
+        if elapsed < interval:
+            self.wait_time = interval - elapsed
         else:
             self.wait_time = self.FAST_START_INTERVAL
 

sonic-thermalctld/tests/test_thermalctld.py

@@ -651,12 +651,14 @@ def test_signal_handler():
 def test_daemon_run():
     daemon_thermalctld = thermalctld.ThermalControlDaemon()
     daemon_thermalctld.stop_event.wait = mock.MagicMock(return_value=True)
+    daemon_thermalctld.thermal_manager.get_interval = mock.MagicMock(return_value=60)
     ret = daemon_thermalctld.run()
     daemon_thermalctld.deinit() # Deinit becuase the test will hang if we assert
     assert ret is False
 
     daemon_thermalctld = thermalctld.ThermalControlDaemon()
     daemon_thermalctld.stop_event.wait = mock.MagicMock(return_value=False)
+    daemon_thermalctld.thermal_manager.get_interval = mock.MagicMock(return_value=60)
     ret = daemon_thermalctld.run()
     daemon_thermalctld.deinit() # Deinit becuase the test will hang if we assert
     assert ret is True