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 <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Weilin Wang <weilin.wang@intel.com>
Link: https://lore.kernel.org/r/20250512184700.11691-1-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 10 insertions, 2 deletions

diff --git a/tools/perf/builtin-list.c b/tools/perf/builtin-list.c
index fed482adb039..e9b595d75df2 100644
--- a/tools/perf/builtin-list.c
+++ b/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);
 }