perf metricgroups: Add NO_THRESHOLD_AND_NMI constraint

Thresholds can increase the number of counters a metric needs. The NMI
watchdog can take away a counter (hopefully the buddy watchdog will
become the default and this will no longer be true). Add a new
constraint for the case that a metric and its thresholds would fit in
counters but only if the NMI watchdog isn't enabled. Either the
threshold or the NMI watchdog should be disabled to make the metric
fit. Wire this up into the metric__group_events logic.

Signed-off-by: Ian Rogers <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Namhyung Kim <[e-mail]>

tools/perf/pmu-events/jevents.py

···
           'NO_GROUP_EVENTS_NMI': '2',
           'NO_NMI_WATCHDOG': '2',
           'NO_GROUP_EVENTS_SMT': '3',
+          'NO_THRESHOLD_AND_NMI': '4',
       }
       return metric_constraint_to_enum[metric_constraint]
 

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

···
 	 */
 	MetricNoGroupEvents = 1,
 	/**
-	 * @MetricNoGroupEventsNmi: Don't group events for the metric if the NMI
-	 *                          watchdog is enabled.
+	 * @MetricNoGroupEventsNmi:
+	 * Don't group events for the metric if the NMI watchdog is enabled.
 	 */
 	MetricNoGroupEventsNmi = 2,
 	/**
-	 * @MetricNoGroupEventsSmt: Don't group events for the metric if SMT is
-	 *                          enabled.
+	 * @MetricNoGroupEventsSmt:
+	 * Don't group events for the metric if SMT is enabled.
 	 */
 	MetricNoGroupEventsSmt = 3,
+	/**
+	 * @MetricNoGroupEventsThresholdAndNmi:
+	 * Don't group events for the metric thresholds and if the NMI watchdog
+	 * is enabled.
+	 */
+	MetricNoGroupEventsThresholdAndNmi = 4,
 };
 /*
  * Describe each PMU event. Each CPU has a table of PMU events.

tools/perf/util/metricgroup.c

···
 		   "    echo 1 > /proc/sys/kernel/nmi_watchdog\n");
 }
 
-static bool metric__group_events(const struct pmu_metric *pm)
+static bool metric__group_events(const struct pmu_metric *pm, bool metric_no_threshold)
 {
 	switch (pm->event_grouping) {
 	case MetricNoGroupEvents:
···
 		return false;
 	case MetricNoGroupEventsSmt:
 		return !smt_on();
+	case MetricNoGroupEventsThresholdAndNmi:
+		if (metric_no_threshold)
+			return true;
+		if (!sysctl__nmi_watchdog_enabled())
+			return true;
+		metric__watchdog_constraint_hint(pm->metric_name, /*foot=*/false);
+		return false;
 	case MetricGroupEvents:
 	default:
 		return true;
···
 static struct metric *metric__new(const struct pmu_metric *pm,
 				  const char *modifier,
 				  bool metric_no_group,
+				  bool metric_no_threshold,
 				  int runtime,
 				  const char *user_requested_cpu_list,
 				  bool system_wide)
···
 	}
 	m->pctx->sctx.runtime = runtime;
 	m->pctx->sctx.system_wide = system_wide;
-	m->group_events = !metric_no_group && metric__group_events(pm);
+	m->group_events = !metric_no_group && metric__group_events(pm, metric_no_threshold);
 	m->metric_refs = NULL;
 	m->evlist = NULL;
 
···
 		 * This metric is the root of a tree and may reference other
 		 * metrics that are added recursively.
 		 */
-		root_metric = metric__new(pm, modifier, metric_no_group, runtime,
-					  user_requested_cpu_list, system_wide);
+		root_metric = metric__new(pm, modifier, metric_no_group, metric_no_threshold,
+					  runtime, user_requested_cpu_list, system_wide);
 		if (!root_metric)
 			return -ENOMEM;