diff --git a/tools/perf/util/metricgroup.h b/tools/perf/util/metricgroup.h
index 88ba939a3082..3a51a84f440b 100644
--- a/tools/perf/util/metricgroup.h
+++ b/tools/perf/util/metricgroup.h
@@ -14,24 +14,51 @@ struct rblist;
 struct pmu_events_map;
 struct cgroup;
 
+/**
+ * A node in a rblist keyed by the evsel. The global rblist of metric events
+ * generally exists in perf_stat_config. The evsel is looked up in the rblist
+ * yielding a list of metric_expr.
+ */
 struct metric_event {
 	struct rb_node nd;
 	struct evsel *evsel;
 	struct list_head head; /* list of metric_expr */
 };
 
+/**
+ * A metric referenced by a metric_expr. When parsing a metric expression IDs
+ * will be looked up, matching either a value (from metric_events) or a
+ * metric_ref. A metric_ref will then be parsed recursively. The metric_refs and
+ * metric_events need to be known before parsing so that their values may be
+ * placed in the parse context for lookup.
+ */
 struct metric_ref {
 	const char *metric_name;
 	const char *metric_expr;
 };
 
+/**
+ * One in a list of metric_expr associated with an evsel. The data is used to
+ * generate a metric value during stat output.
+ */
 struct metric_expr {
 	struct list_head nd;
+	/** The expression to parse, for example, "instructions/cycles". */
 	const char *metric_expr;
+	/** The name of the meric such as "IPC". */
 	const char *metric_name;
+	/**
+	 * The "ScaleUnit" that scales and adds a unit to the metric during
+	 * output. For example, "6.4e-05MiB" means to scale the resulting metric
+	 * by 6.4e-05 (typically converting a unit like cache lines to something
+	 * more human intelligible) and then add "MiB" afterward when displayed.
+	 */
 	const char *metric_unit;
+	/** Null terminated array of events used by the metric. */
 	struct evsel **metric_events;
+	/** Null terminated array of referenced metrics. */
 	struct metric_ref *metric_refs;
+	/** A value substituted for '?' during parsing. */
 	int runtime;
 };