Bug 1726657 - Only record sampling overheads if MOZ_PROFILER_RECORD_OVERHEADS is set - r=florian

Sampling overheads are very rarely useful, but they occupy some space during profiling, but also a lot of space in the final JSON profile.
So now they will only be recorded if the environment variable "MOZ_PROFILER_RECORD_OVERHEADS" is set to any non-empty value.

Differential Revision: https://phabricator.services.mozilla.com/D123303

mozglue/baseprofiler/core/ProfileBuffer.cpp

@@ -161,12 +161,18 @@ void ProfileBuffer::CollectOverheadStats(TimeDuration aSamplingTime,
   mCountersUs.Count(countersUs);
   mThreadsUs.Count(threadsUs);
 
-  // Record details in buffer.
-  AddEntry(ProfileBufferEntry::ProfilerOverheadTime(timeUs));
-  AddEntry(ProfileBufferEntry::ProfilerOverheadDuration(lockingUs));
-  AddEntry(ProfileBufferEntry::ProfilerOverheadDuration(cleaningUs));
-  AddEntry(ProfileBufferEntry::ProfilerOverheadDuration(countersUs));
-  AddEntry(ProfileBufferEntry::ProfilerOverheadDuration(threadsUs));
+  // Record details in buffer, if requested.
+  static const bool sRecordSamplingOverhead = []() {
+    const char* recordOverheads = getenv("MOZ_PROFILER_RECORD_OVERHEADS");
+    return recordOverheads && recordOverheads[0] != '\0';
+  }();
+  if (sRecordSamplingOverhead) {
+    AddEntry(ProfileBufferEntry::ProfilerOverheadTime(timeUs));
+    AddEntry(ProfileBufferEntry::ProfilerOverheadDuration(lockingUs));
+    AddEntry(ProfileBufferEntry::ProfilerOverheadDuration(cleaningUs));
+    AddEntry(ProfileBufferEntry::ProfilerOverheadDuration(countersUs));
+    AddEntry(ProfileBufferEntry::ProfilerOverheadDuration(threadsUs));
+  }
 }
 
 ProfilerBufferInfo ProfileBuffer::GetProfilerBufferInfo() const {

tools/profiler/core/ProfileBuffer.cpp

@@ -156,11 +156,17 @@ void ProfileBuffer::CollectOverheadStats(double aSamplingTimeMs,
   mCountersUs.Count(counters);
   mThreadsUs.Count(threads);
 
-  AddEntry(ProfileBufferEntry::ProfilerOverheadTime(aSamplingTimeMs));
-  AddEntry(ProfileBufferEntry::ProfilerOverheadDuration(locking));
-  AddEntry(ProfileBufferEntry::ProfilerOverheadDuration(cleaning));
-  AddEntry(ProfileBufferEntry::ProfilerOverheadDuration(counters));
-  AddEntry(ProfileBufferEntry::ProfilerOverheadDuration(threads));
+  static const bool sRecordSamplingOverhead = []() {
+    const char* recordOverheads = getenv("MOZ_PROFILER_RECORD_OVERHEADS");
+    return recordOverheads && recordOverheads[0] != '\0';
+  }();
+  if (sRecordSamplingOverhead) {
+    AddEntry(ProfileBufferEntry::ProfilerOverheadTime(aSamplingTimeMs));
+    AddEntry(ProfileBufferEntry::ProfilerOverheadDuration(locking));
+    AddEntry(ProfileBufferEntry::ProfilerOverheadDuration(cleaning));
+    AddEntry(ProfileBufferEntry::ProfilerOverheadDuration(counters));
+    AddEntry(ProfileBufferEntry::ProfilerOverheadDuration(threads));
+  }
 }
 
 ProfilerBufferInfo ProfileBuffer::GetProfilerBufferInfo() const {