perf tools: Cache counter names for raw samples on s390

Searching all event names is slower now that legacy names are
included. Add a cache to avoid long iterative searches. Note, the
cache isn't cleaned up and is as such a memory leak, however, globally
reachable leaks like this aren't treated as leaks by leak sanitizer.

Reported-by: Thomas Richter <[e-mail]>
Closes: https://lore.kernel.org/linux-perf-users/[e-mail]/
Signed-off-by: Ian Rogers <[e-mail]>
Tested-by: Thomas Richter <[e-mail]>
Signed-off-by: Namhyung Kim <[e-mail]>

tools/perf/util/s390-sample-raw.c

···
 
 #include <sys/stat.h>
 #include <linux/compiler.h>
+#include <linux/err.h>
 #include <asm/byteorder.h>
 
 #include "debug.h"
 #include "session.h"
 #include "evlist.h"
 #include "color.h"
+#include "hashmap.h"
 #include "sample-raw.h"
 #include "s390-cpumcf-kernel.h"
 #include "util/pmu.h"
···
 }
 
 struct get_counter_name_data {
-	int wanted;
-	char *result;
+	long wanted;
+	const char *result;
 };
 
 static int get_counter_name_callback(void *vdata, struct pmu_event_info *info)
···
 
 	rc = sscanf(event_str, "event=%x", &event_nr);
 	if (rc == 1 && event_nr == data->wanted) {
-		data->result = strdup(info->name);
+		data->result = info->name;
 		return 1; /* Terminate the search. */
 	}
 	return 0;
+}
+
+static size_t get_counter_name_hash_fn(long key, void *ctx __maybe_unused)
+{
+	return key;
+}
+
+static bool get_counter_name_hashmap_equal_fn(long key1, long key2, void *ctx __maybe_unused)
+{
+	return key1 == key2;
 }
 
 /* Scan the PMU and extract the logical name of a counter from the event. Input
···
  */
 static char *get_counter_name(int set, int nr, struct perf_pmu *pmu)
 {
+	static struct hashmap *cache;
+	static struct perf_pmu *cache_pmu;
+	long cache_key = get_counterset_start(set) + nr;
 	struct get_counter_name_data data = {
-		.wanted = get_counterset_start(set) + nr,
+		.wanted = cache_key,
 		.result = NULL,
 	};
+	char *result = NULL;
 
 	if (!pmu)
 		return NULL;
 
+	if (cache_pmu == pmu && hashmap__find(cache, cache_key, &result))
+		return strdup(result);
+
 	perf_pmu__for_each_event(pmu, /*skip_duplicate_pmus=*/ true,
 				 &data, get_counter_name_callback);
-	return data.result;
+
+	result = strdup(data.result ?: "<unknown>");
+
+	if (cache_pmu == NULL) {
+		struct hashmap *tmp = hashmap__new(get_counter_name_hash_fn,
+						   get_counter_name_hashmap_equal_fn,
+						   /*ctx=*/NULL);
+
+		if (!IS_ERR(tmp)) {
+			cache = tmp;
+			cache_pmu = pmu;
+		}
+	}
+
+	if (cache_pmu == pmu && result) {
+		char *old_value = NULL, *new_value = strdup(result);
+
+		if (new_value) {
+			hashmap__set(cache, cache_key, new_value, /*old_key=*/NULL, &old_value);
+			/*
+			 * Free in case of a race, but resizing would be broken
+			 * in that case.
+			 */
+			free(old_value);
+		}
+	}
+	return result;
 }
 
 static void s390_cpumcfdg_dump(struct perf_pmu *pmu, struct perf_sample *sample)