perf list: Display the PMU name associated with a perf metric in JSON

The 'perf stat --cputype' option can be used to filter which metrics
will be applied, for this reason the JSON metrics have an associated
PMU.

List this PMU name in the 'perf list' output in JSON mode so that
tooling may access it.

An example of the new field is:
```
{
        "MetricGroup": "Backend",
        "MetricName": "tma_core_bound",
        "MetricExpr": "max(0, tma_backend_bound - tma_memory_bound)",
        "MetricThreshold": "tma_core_bound > 0.1 & tma_backend_bound > 0.2",
        "ScaleUnit": "100%",
        "BriefDescription": "This metric represents fraction of slots where ...
        "PublicDescription": "This metric represents fraction of slots where ...
        "Unit": "cpu_core"
},
```

Signed-off-by: Ian Rogers <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: James Clark <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Kan Liang <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Weilin Wang <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

Author: captain5050

tools/perf/builtin-list.c

@@ -197,7 +197,8 @@ static void default_print_metric(void *ps,
 				const char *long_desc,
 				const char *expr,
 				const char *threshold,
-				const char *unit __maybe_unused)
+				const char *unit __maybe_unused,
+				const char *pmu_name __maybe_unused)
 {
 	struct print_state *print_state = ps;
 	FILE *fp = print_state->fp;
@@ -433,7 +434,8 @@ static void json_print_event(void *ps, const char *topic, const char *pmu_name,
 static void json_print_metric(void *ps __maybe_unused, const char *group,
 			      const char *name, const char *desc,
 			      const char *long_desc, const char *expr,
-			      const char *threshold, const char *unit)
+			      const char *threshold, const char *unit,
+			      const char *pmu_name)
 {
 	struct json_print_state *print_state = ps;
 	bool need_sep = false;
@@ -483,6 +485,12 @@ static void json_print_metric(void *ps __maybe_unused, const char *group,
 				   long_desc);
 		need_sep = true;
 	}
+	if (pmu_name) {
+		fix_escape_fprintf(fp, &buf, "%s\t\"Unit\": \"%S\"",
+				   need_sep ? ",\n" : "",
+				   pmu_name);
+		need_sep = true;
+	}
 	fprintf(fp, "%s}", need_sep ? "\n" : "");
 	strbuf_release(&buf);
 }

tools/perf/util/metricgroup.c

@@ -396,6 +396,7 @@ struct mep {
 	const char *metric_expr;
 	const char *metric_threshold;
 	const char *metric_unit;
+	const char *pmu_name;
 };
 
 static int mep_cmp(struct rb_node *rb_node, const void *entry)
@@ -476,6 +477,7 @@ static int metricgroup__add_to_mep_groups(const struct pmu_metric *pm,
 			me->metric_expr = pm->metric_expr;
 			me->metric_threshold = pm->metric_threshold;
 			me->metric_unit = pm->unit;
+			me->pmu_name = pm->pmu;
 		}
 	}
 	free(omg);
@@ -551,7 +553,8 @@ void metricgroup__print(const struct print_callbacks *print_cb, void *print_stat
 				me->metric_long_desc,
 				me->metric_expr,
 				me->metric_threshold,
-				me->metric_unit);
+				me->metric_unit,
+				me->pmu_name);
 		next = rb_next(node);
 		rblist__remove_node(&groups, node);
 	}

tools/perf/util/print-events.h

@@ -25,7 +25,8 @@ struct print_callbacks {
 			const char *long_desc,
 			const char *expr,
 			const char *threshold,
-			const char *unit);
+			const char *unit,
+			const char *pmu_name);
 	bool (*skip_duplicate_pmus)(void *print_state);
 };