perf parse-events: Warn if a cpu term is unsupported by a CPU

Factor requested CPU warning out of evlist and into evsel. At the end
of adding an event, perform the warning check. To avoid repeatedly
testing if the cpu_list is empty, add a local variable.

```
$ perf stat -e cpu_atom/cycles,cpu=1/ -a true
WARNING: A requested CPU in '1' is not supported by PMU 'cpu_atom' (CPUs 16-27) for event 'cpu_atom/cycles/'

 Performance counter stats for 'system wide':

   <not supported>      cpu_atom/cycles/

       0.000781511 seconds time elapsed
```

Reviewed-by: Thomas Falcon <thomas.falcon@intel.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: James Clark <james.clark@linaro.org>
Link: https://lore.kernel.org/r/20250719030517.1990983-2-irogers@google.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

tools/perf/util/evlist.c

@@ -2549,20 +2549,7 @@ void evlist__warn_user_requested_cpus(struct evlist *evlist, const char *cpu_lis
 		return;
 
 	evlist__for_each_entry(evlist, pos) {
-		struct perf_cpu_map *intersect, *to_test, *online = cpu_map__online();
-		const struct perf_pmu *pmu = evsel__find_pmu(pos);
-
-		to_test = pmu && pmu->is_core ? pmu->cpus : online;
-		intersect = perf_cpu_map__intersect(to_test, user_requested_cpus);
-		if (!perf_cpu_map__equal(intersect, user_requested_cpus)) {
-			char buf[128];
-
-			cpu_map__snprint(to_test, buf, sizeof(buf));
-			pr_warning("WARNING: A requested CPU in '%s' is not supported by PMU '%s' (CPUs %s) for event '%s'\n",
-				cpu_list, pmu ? pmu->name : "cpu", buf, evsel__name(pos));
-		}
-		perf_cpu_map__put(intersect);
-		perf_cpu_map__put(online);
+		evsel__warn_user_requested_cpus(pos, user_requested_cpus);
 	}
 	perf_cpu_map__put(user_requested_cpus);
 }

tools/perf/util/evsel.c

@@ -4091,3 +4091,27 @@ void evsel__uniquify_counter(struct evsel *counter)
 		counter->uniquified_name = false;
 	}
 }
+
+void evsel__warn_user_requested_cpus(struct evsel *evsel, struct perf_cpu_map *user_requested_cpus)
+{
+	struct perf_cpu_map *intersect, *online = NULL;
+	const struct perf_pmu *pmu = evsel__find_pmu(evsel);
+
+	if (pmu && pmu->is_core) {
+		intersect = perf_cpu_map__intersect(pmu->cpus, user_requested_cpus);
+	} else {
+		online = cpu_map__online();
+		intersect = perf_cpu_map__intersect(online, user_requested_cpus);
+	}
+	if (!perf_cpu_map__equal(intersect, user_requested_cpus)) {
+		char buf1[128];
+		char buf2[128];
+
+		cpu_map__snprint(user_requested_cpus, buf1, sizeof(buf1));
+		cpu_map__snprint(online ?: pmu->cpus, buf2, sizeof(buf2));
+		pr_warning("WARNING: A requested CPU in '%s' is not supported by PMU '%s' (CPUs %s) for event '%s'\n",
+			   buf1, pmu ? pmu->name : "cpu", buf2, evsel__name(evsel));
+	}
+	perf_cpu_map__put(intersect);
+	perf_cpu_map__put(online);
+}

tools/perf/util/evsel.h

@@ -574,4 +574,6 @@ void evsel__set_config_if_unset(struct perf_pmu *pmu, struct evsel *evsel,
 
 bool evsel__is_offcpu_event(struct evsel *evsel);
 
+void evsel__warn_user_requested_cpus(struct evsel *evsel, struct perf_cpu_map *user_requested_cpus);
+
 #endif /* __PERF_EVSEL_H */

tools/perf/util/parse-events.c

@@ -252,6 +252,7 @@ __add_event(struct list_head *list, int *idx,
 	struct evsel *evsel;
 	bool is_pmu_core;
 	struct perf_cpu_map *cpus;
+	bool has_cpu_list = !perf_cpu_map__is_empty(cpu_list);
 
 	/*
 	 * Ensure the first_wildcard_match's PMU matches that of the new event
@@ -276,7 +277,7 @@ __add_event(struct list_head *list, int *idx,
 
 	if (pmu) {
 		is_pmu_core = pmu->is_core;
-		cpus = perf_cpu_map__get(perf_cpu_map__is_empty(cpu_list) ? pmu->cpus : cpu_list);
+		cpus = perf_cpu_map__get(has_cpu_list ? cpu_list : pmu->cpus);
 		perf_pmu__warn_invalid_formats(pmu);
 		if (attr->type == PERF_TYPE_RAW || attr->type >= PERF_TYPE_MAX) {
 			perf_pmu__warn_invalid_config(pmu, attr->config, name,
@@ -291,10 +292,10 @@ __add_event(struct list_head *list, int *idx,
 	} else {
 		is_pmu_core = (attr->type == PERF_TYPE_HARDWARE ||
 			       attr->type == PERF_TYPE_HW_CACHE);
-		if (perf_cpu_map__is_empty(cpu_list))
-			cpus = is_pmu_core ? perf_cpu_map__new_online_cpus() : NULL;
-		else
+		if (has_cpu_list)
 			cpus = perf_cpu_map__get(cpu_list);
+		else
+			cpus = is_pmu_core ? cpu_map__online() : NULL;
 	}
 	if (init_attr)
 		event_attr_init(attr);
@@ -326,6 +327,9 @@ __add_event(struct list_head *list, int *idx,
 	if (list)
 		list_add_tail(&evsel->core.node, list);
 
+	if (has_cpu_list)
+		evsel__warn_user_requested_cpus(evsel, cpu_list);
+
 	return evsel;
 }