perf metric: Comment data structures

Document the data structures maintained by metricgroup.c and used by
stat-shadow.c for metric output.

Signed-off-by: Ian Rogers <irogers@google.com>
Acked-by: Andi Kleen <ak@linux.intel.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Antonov <alexander.antonov@linux.intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andrew Kilroy <andrew.kilroy@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Changbin Du <changbin.du@intel.com>
Cc: Denys Zagorui <dzagorui@cisco.com>
Cc: Fabian Hemmer <copy@copy.sh>
Cc: Felix Fietkau <nbd@nbd.name>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jacob Keller <jacob.e.keller@intel.com>
Cc: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Joakim Zhang <qiangqing.zhang@nxp.com>
Cc: John Garry <john.garry@huawei.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Kees Kook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Nicholas Fraser <nfraser@codeweavers.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Paul Clarke <pc@us.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Riccardo Mancini <rickyman7@gmail.com>
Cc: Sami Tolvanen <samitolvanen@google.com>
Cc: ShihCheng Tu <mrtoastcheng@gmail.com>
Cc: Song Liu <songliubraving@fb.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Sumanth Korikkar <sumanthk@linux.ibm.com>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Cc: Wan Jiabing <wanjiabing@vivo.com>
Cc: Zhen Lei <thunder.leizhen@huawei.com>
Link: https://lore.kernel.org/r/20211015172132.1162559-11-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

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;
 };