perf parse-events: Avoid scanning PMUs that can't contain events

JIRA: https://issues.redhat.com/browse/RHEL-78200

upstream
========
commit e1ec69e
Author: Ian Rogers <irogers@google.com>
Date: Tue Jun 24 16:18:35 2025 -0700

description
===========
Add perf_pmus__scan_for_event that only reads sysfs for pmus that
could contain a given event.

    Signed-off-by: Ian Rogers <irogers@google.com>
    Link: https://lore.kernel.org/r/20250624231837.179536-2-irogers@google.com
    Signed-off-by: Namhyung Kim <namhyung@kernel.org>

Signed-off-by: Anubhav Shelat <ashelat@redhat.com>

Author: AnubhavS1

tools/perf/util/parse-events.c

@@ -485,7 +485,7 @@ int parse_events_add_cache(struct list_head *list, int *idx, const char *name,
 	int ret = 0;
 	struct evsel *first_wildcard_match = NULL;
 
-	while ((pmu = perf_pmus__scan(pmu)) != NULL) {
+	while ((pmu = perf_pmus__scan_for_event(pmu, name)) != NULL) {
 		LIST_HEAD(config_terms);
 		struct perf_event_attr attr;
 
@@ -1676,7 +1676,8 @@ int parse_events_multi_pmu_add(struct parse_events_state *parse_state,
 
 	INIT_LIST_HEAD(list);
 
-	while ((pmu = perf_pmus__scan(pmu)) != NULL) {
+	while ((pmu = perf_pmus__scan_for_event(pmu, event_name)) != NULL) {
+
 		if (parse_events__filter_pmu(parse_state, pmu))
 			continue;
 
@@ -1755,19 +1756,21 @@ int parse_events_multi_pmu_add_or_add_pmu(struct parse_events_state *parse_state
 
 	pmu = NULL;
 	/* Failed to add, try wildcard expansion of event_or_pmu as a PMU name. */
-	while ((pmu = perf_pmus__scan(pmu)) != NULL) {
-		if (!parse_events__filter_pmu(parse_state, pmu) &&
-		    perf_pmu__wildcard_match(pmu, event_or_pmu)) {
-			if (!parse_events_add_pmu(parse_state, *listp, pmu,
-						  const_parsed_terms,
-						  first_wildcard_match,
-						  /*alternate_hw_config=*/PERF_COUNT_HW_MAX)) {
-				ok++;
-				parse_state->wild_card_pmus = true;
-			}
-			if (first_wildcard_match == NULL)
-				first_wildcard_match =
-					container_of((*listp)->prev, struct evsel, core.node);
+	while ((pmu = perf_pmus__scan_matching_wildcard(pmu, event_or_pmu)) != NULL) {
+
+		if (parse_events__filter_pmu(parse_state, pmu))
+			continue;
+
+		if (!parse_events_add_pmu(parse_state, *listp, pmu,
+					  const_parsed_terms,
+					  first_wildcard_match,
+					  /*alternate_hw_config=*/PERF_COUNT_HW_MAX)) {
+			ok++;
+			parse_state->wild_card_pmus = true;
+		}
+		if (first_wildcard_match == NULL) {
+			first_wildcard_match =
+				container_of((*listp)->prev, struct evsel, core.node);
 		}
 	}
 	if (ok)

tools/perf/util/pmus.c

@@ -19,6 +19,7 @@
 #include "tool_pmu.h"
 #include "print-events.h"
 #include "strbuf.h"
+#include "string2.h"
 
 /*
  * core_pmus:  A PMU belongs to core_pmus if it's name is "cpu" or it's sysfs
@@ -350,6 +351,82 @@ struct perf_pmu *perf_pmus__scan_core(struct perf_pmu *pmu)
 	return NULL;
 }
 
+struct perf_pmu *perf_pmus__scan_for_event(struct perf_pmu *pmu, const char *event)
+{
+	bool use_core_pmus = !pmu || pmu->is_core;
+
+	if (!pmu) {
+		/* Hwmon filename values that aren't used. */
+		enum hwmon_type type;
+		int number;
+		/*
+		 * Core PMUs, other sysfs PMUs and tool PMU can take all event
+		 * types or aren't wother optimizing for.
+		 */
+		unsigned int to_read_pmus =  PERF_TOOL_PMU_TYPE_PE_CORE_MASK |
+			PERF_TOOL_PMU_TYPE_PE_OTHER_MASK |
+			PERF_TOOL_PMU_TYPE_TOOL_MASK;
+
+		/* Could the event be a hwmon event? */
+		if (parse_hwmon_filename(event, &type, &number, /*item=*/NULL, /*alarm=*/NULL))
+			to_read_pmus |= PERF_TOOL_PMU_TYPE_HWMON_MASK;
+
+		pmu_read_sysfs(to_read_pmus);
+		pmu = list_prepare_entry(pmu, &core_pmus, list);
+	}
+	if (use_core_pmus) {
+		list_for_each_entry_continue(pmu, &core_pmus, list)
+			return pmu;
+
+		pmu = NULL;
+		pmu = list_prepare_entry(pmu, &other_pmus, list);
+	}
+	list_for_each_entry_continue(pmu, &other_pmus, list)
+		return pmu;
+	return NULL;
+}
+
+struct perf_pmu *perf_pmus__scan_matching_wildcard(struct perf_pmu *pmu, const char *wildcard)
+{
+	bool use_core_pmus = !pmu || pmu->is_core;
+
+	if (!pmu) {
+		/*
+		 * Core PMUs, other sysfs PMUs and tool PMU can have any name or
+		 * aren't wother optimizing for.
+		 */
+		unsigned int to_read_pmus =  PERF_TOOL_PMU_TYPE_PE_CORE_MASK |
+			PERF_TOOL_PMU_TYPE_PE_OTHER_MASK |
+			PERF_TOOL_PMU_TYPE_TOOL_MASK;
+
+		/*
+		 * Hwmon PMUs have an alias from a sysfs name like hwmon0,
+		 * hwmon1, etc. or have a name of hwmon_<name>. They therefore
+		 * can only have a wildcard match if the wildcard begins with
+		 * "hwmon".
+		 */
+		if (strisglob(wildcard) ||
+		    (strlen(wildcard) >= 5 && strncmp("hwmon", wildcard, 5) == 0))
+			to_read_pmus |= PERF_TOOL_PMU_TYPE_HWMON_MASK;
+
+		pmu_read_sysfs(to_read_pmus);
+		pmu = list_prepare_entry(pmu, &core_pmus, list);
+	}
+	if (use_core_pmus) {
+		list_for_each_entry_continue(pmu, &core_pmus, list) {
+			if (perf_pmu__wildcard_match(pmu, wildcard))
+				return pmu;
+		}
+		pmu = NULL;
+		pmu = list_prepare_entry(pmu, &other_pmus, list);
+	}
+	list_for_each_entry_continue(pmu, &other_pmus, list) {
+		if (perf_pmu__wildcard_match(pmu, wildcard))
+			return pmu;
+	}
+	return NULL;
+}
+
 static struct perf_pmu *perf_pmus__scan_skip_duplicates(struct perf_pmu *pmu)
 {
 	bool use_core_pmus = !pmu || pmu->is_core;

tools/perf/util/pmus.h

@@ -19,6 +19,8 @@ struct perf_pmu *perf_pmus__find_by_type(unsigned int type);
 
 struct perf_pmu *perf_pmus__scan(struct perf_pmu *pmu);
 struct perf_pmu *perf_pmus__scan_core(struct perf_pmu *pmu);
+struct perf_pmu *perf_pmus__scan_for_event(struct perf_pmu *pmu, const char *event);
+struct perf_pmu *perf_pmus__scan_matching_wildcard(struct perf_pmu *pmu, const char *wildcard);
 
 const struct perf_pmu *perf_pmus__pmu_for_pmu_filter(const char *str);