perf jevents: Add support for metricgroup descriptions

Metrics have a field where the groups they belong to are listed like
the following from
tools/perf/pmu-events/arch/x86/skylakex/skx-metrics.json:

        "MetricGroup": "PGO;TmaL1;TopdownL1;tma_L1_group",
        "MetricName": "tma_frontend_bound",

The metric groups are shown in 'perf list' like the following where
TopdownL1 is a metric group:

TopdownL1:
  tma_backend_bound
       [This category represents fraction of slots where no uops are being
        delivered due to a lack of required resources for accepting new uops
        in the Backend]
  tma_bad_speculation
       [This category represents fraction of slots wasted due to incorrect
        speculations]
  tma_frontend_bound
       [This category represents fraction of slots where the processor's
        Frontend undersupplies its Backend]
  tma_retiring
       [This category represents fraction of slots utilized by useful work
        i.e. issued uops that eventually get retired]

This patch adds support for a new json file in each model directory
called metricgroups.json that comprises a dictionary containing
entries that map from a metric group to a description:

{
...
    "TopdownL1": "Metrics for top-down breakdown at level 1",
...
}

perf list is then updated to support this changing the above output
to:

  TopdownL1: [Metrics for top-down breakdown at level 1]

Committer notes:

Added a (int) cast to the ARRAY_SIZE() introduced in this patch to
address:

  /tmp/build/perf-tools-next/pmu-events/pmu-events.c: In function ‘describe_metricgroup’:
  /var/home/acme/git/perf-tools-next/tools/include/linux/kernel.h:102:25: error: overflow in conversion from ‘long unsigned int’ to ‘int’ changes value from ‘18446744073709551615’ to ‘-1’ [-Werror=overflow]
    102 | #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) + __must_be_array(arr))
        |                         ^
  /tmp/build/perf-tools-next/pmu-events/pmu-events.c:61603:29: note: in expansion of macro ‘ARRAY_SIZE’
  61603 |         int low = 0, high = ARRAY_SIZE(metricgroups) - 1;
        |                             ^~~~~~~~~~
  cc1: all warnings being treated as errors

Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
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: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.g.garry@oracle.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Cc: Xing Zhengjun <zhengjun.xing@linux.intel.com>
Link: https://lore.kernel.org/r/20230517173805.602113-15-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-list.c

@@ -192,9 +192,14 @@ static void default_print_metric(void *ps,
 		if (group && print_state->metricgroups) {
 			if (print_state->name_only)
 				printf("%s ", group);
-			else if (print_state->metrics)
-				printf("\n%s:\n", group);
+			else if (print_state->metrics) {
+				const char *gdesc = describe_metricgroup(group);
+
+				if (gdesc)
+					printf("\n%s: [%s]\n", group, gdesc);
 				else
+					printf("\n%s:\n", group);
+			} else
 				printf("%s\n", group);
 		}
 		zfree(&print_state->last_metricgroups);

tools/perf/pmu-events/empty-pmu-events.c

@@ -420,3 +420,8 @@ int pmu_for_each_sys_metric(pmu_metric_iter_fn fn __maybe_unused, void *data __m
 {
 	return 0;
 }
+
+const char *describe_metricgroup(const char *group __maybe_unused)
+{
+	return NULL;
+}

tools/perf/pmu-events/jevents.py

@@ -37,6 +37,8 @@ _pending_metrics = []
 _pending_metrics_tblname = None
 # Global BigCString shared by all structures.
 _bcs = None
+# Map from the name of a metric group to a description of the group.
+_metricgroups = {}
 # Order specific JsonEvent attributes will be visited.
 _json_event_attributes = [
     # cmp_sevent related attributes.
@@ -512,6 +514,17 @@ def preprocess_one_file(parents: Sequence[str], item: os.DirEntry) -> None:
   if not item.is_file() or not item.name.endswith('.json'):
     return
 
+  if item.name == 'metricgroups.json':
+    metricgroup_descriptions = json.load(open(item.path))
+    for mgroup in metricgroup_descriptions:
+      assert len(mgroup) > 1, parents
+      description = f"{metricgroup_descriptions[mgroup]}\\000"
+      mgroup = f"{mgroup}\\000"
+      _bcs.add(mgroup)
+      _bcs.add(description)
+      _metricgroups[mgroup] = description
+    return
+
   topic = get_topic(item.name)
   for event in read_json_events(item.path, topic):
     if event.name:
@@ -548,7 +561,7 @@ def process_one_file(parents: Sequence[str], item: os.DirEntry) -> None:
 
   # Ignore other directories. If the file name does not have a .json
   # extension, ignore it. It could be a readme.txt for instance.
-  if not item.is_file() or not item.name.endswith('.json'):
+  if not item.is_file() or not item.name.endswith('.json') or item.name == 'metricgroups.json':
     return
 
   add_events_table_entries(item, get_topic(item.name))
@@ -911,6 +924,38 @@ int pmu_for_each_sys_metric(pmu_metric_iter_fn fn, void *data)
 }
 """)
 
+def print_metricgroups() -> None:
+  _args.output_file.write("""
+static const int metricgroups[][2] = {
+""")
+  for mgroup in sorted(_metricgroups):
+    description = _metricgroups[mgroup]
+    _args.output_file.write(
+        f'\t{{ {_bcs.offsets[mgroup]}, {_bcs.offsets[description]} }}, /* {mgroup} => {description} */\n'
+    )
+  _args.output_file.write("""
+};
+
+const char *describe_metricgroup(const char *group)
+{
+        int low = 0, high = (int)ARRAY_SIZE(metricgroups) - 1;
+
+        while (low <= high) {
+                int mid = (low + high) / 2;
+                const char *mgroup = &big_c_string[metricgroups[mid][0]];
+                int cmp = strcmp(mgroup, group);
+
+                if (cmp == 0) {
+                        return &big_c_string[metricgroups[mid][1]];
+                } else if (cmp < 0) {
+                        low = mid + 1;
+                } else {
+                        high = mid - 1;
+                }
+        }
+        return NULL;
+}
+""")
 
 def main() -> None:
   global _args
@@ -993,7 +1038,7 @@ struct compact_pmu_event {
 
   print_mapping_table(archs)
   print_system_mapping_table()
-
+  print_metricgroups()
 
 if __name__ == '__main__':
   main()

tools/perf/pmu-events/pmu-events.h

@@ -93,4 +93,6 @@ const struct pmu_metrics_table *find_sys_metrics_table(const char *name);
 int pmu_for_each_sys_event(pmu_event_iter_fn fn, void *data);
 int pmu_for_each_sys_metric(pmu_metric_iter_fn fn, void *data);
 
+const char *describe_metricgroup(const char *group);
+
 #endif