From eb9e0c98704e700b5c1f54db71a24cac91b233b4 Mon Sep 17 00:00:00 2001
From: Douglas Raillard <douglas.raillard@arm.com>
Date: Mon, 3 Feb 2025 15:51:58 +0000
Subject: [PATCH] collector/ftrace: Make emitting cpu_frequency_devlib and
 extra idle events dependent on the configured events

Make cpu_frequency_devlib dependent on whether the "cpu_frequency" event
has been selected rather than dependent on the cpufreq devlib module
being loaded on the target.

The old behavior became particularly problematic with the lazy loading
of modules. However, it was never a reliable way of knowing if the user
was interested in the frequency or not.

Apply a similar mechanism for the extra idle state transitions only done
if "cpu_idle" event is selected.
---
 devlib/collector/ftrace.py | 37 +++++++++++++++++++++++++++++--------
 1 file changed, 29 insertions(+), 8 deletions(-)

diff --git a/devlib/collector/ftrace.py b/devlib/collector/ftrace.py
index ddbc748..e7b5234 100644
--- a/devlib/collector/ftrace.py
+++ b/devlib/collector/ftrace.py
@@ -93,7 +93,6 @@ class FtraceCollector(CollectorBase):
         self.host_binary = None
         self.start_time = None
         self.stop_time = None
-        self.event_string = None
         self.function_string = None
         self.trace_clock = trace_clock
         self.saved_cmdlines_nr = saved_cmdlines_nr
@@ -195,7 +194,11 @@ class FtraceCollector(CollectorBase):
             elif self.tracer == 'function_graph':
                 self.function_string = _build_graph_functions(selected_functions, trace_children_functions)
 
-        self.event_string = _build_trace_events(selected_events)
+        self._selected_events = selected_events
+
+    @property
+    def event_string(self):
+        return _build_trace_events(self._selected_events)
 
     @classmethod
     def _resolve_tracing_path(cls, target, path):
@@ -270,6 +273,26 @@ class FtraceCollector(CollectorBase):
 
         self._reset_needed = False
 
+    def _trace_frequencies(self):
+        if 'cpu_frequency' in self._selected_events:
+            self.logger.debug('Trace CPUFreq frequencies')
+            try:
+                mod = self.target.cpufreq
+            except TargetStableError as e:
+                self.logger.error(f'Could not trace CPUFreq frequencies as the cpufreq module cannot be loaded: {e}')
+            else:
+                mod.trace_frequencies()
+
+    def _trace_idle(self):
+        if 'cpu_idle' in self._selected_events:
+            self.logger.debug('Trace CPUIdle states')
+            try:
+                mod = self.target.cpuidle
+            except TargetStableError as e:
+                self.logger.error(f'Could not trace CPUIdle states as the cpuidle module cannot be loaded: {e}')
+            else:
+                mod.perturb_cpus()
+
     @asyncf
     async def start(self):
         self.start_time = time.time()
@@ -302,12 +325,10 @@ class FtraceCollector(CollectorBase):
         )
         if self.automark:
             self.mark_start()
-        if 'cpufreq' in self.target.modules:
-            self.logger.debug('Trace CPUFreq frequencies')
-            self.target.cpufreq.trace_frequencies()
-        if 'cpuidle' in self.target.modules:
-            self.logger.debug('Trace CPUIdle states')
-            self.target.cpuidle.perturb_cpus()
+
+        self._trace_frequencies()
+        self._trace_idle()
+
         # Enable kernel function profiling
         if self.functions and self.tracer is None:
             target = self.target