diff --git a/services/audioflinger/FastThreadDumpState.h b/services/audioflinger/FastThreadDumpState.h
index bbca7da..1ce0914 100644
--- a/services/audioflinger/FastThreadDumpState.h
+++ b/services/audioflinger/FastThreadDumpState.h
@@ -22,7 +22,12 @@
 
 namespace android {
 
-// FIXME extract common part of comment at FastMixerDumpState
+// The FastThreadDumpState keeps a cache of FastThread statistics that can be logged by dumpsys.
+// Each individual native word-sized field is accessed atomically.  But the
+// overall structure is non-atomic, that is there may be an inconsistency between fields.
+// No barriers or locks are used for either writing or reading.
+// Only POD types are permitted, and the contents shouldn't be trusted (i.e. do range checks).
+// It has a different lifetime than the FastThread, and so it can't be a member of FastThread.
 struct FastThreadDumpState {
     FastThreadDumpState();
     /*virtual*/ ~FastThreadDumpState();