perf pmus: Check if we can encode the PMU number in perf_event_attr.type

In some architectures we can't encode the PMU number in
perf_event_attr.type and thus can't just ask for the same event in
multiple CPUs (and thus PMUs), that is what we want in hybrid systems
but we can't when that encoding isn't understood by the kernel, such as
in ARM64's big.LITTLE.

If that is the case, fallback to the previous behaviour till we find a
better solution to have consistent output accross architectures with
hybrid CPU configurations.

Co-developed-with: Ian Rogers <[email protected]>
Cc: James Clark <[email protected]>
Cc: John Garry <[email protected]>
Cc: Leo Yan <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Mike Leach <[email protected]>
Cc: Sumanth Korikkar <[email protected]>
Cc: Suzuki K Poulose <[email protected]>
Cc: Thomas Richter <[email protected]>
Cc: Will Deacon <[email protected]>
Link: https://lore.kernel.org/linux-perf-users/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

Author: acmel

tools/perf/util/pmus.c

@@ -4,6 +4,7 @@
 #include <subcmd/pager.h>
 #include <sys/types.h>
 #include <dirent.h>
+#include <pthread.h>
 #include <string.h>
 #include <unistd.h>
 #include "debug.h"
@@ -492,9 +493,35 @@ int perf_pmus__num_core_pmus(void)
 	return count;
 }
 
+static bool __perf_pmus__supports_extended_type(void)
+{
+	struct perf_pmu *pmu = NULL;
+
+	if (perf_pmus__num_core_pmus() <= 1)
+		return false;
+
+	while ((pmu = perf_pmus__scan_core(pmu)) != NULL) {
+		if (!is_event_supported(PERF_TYPE_HARDWARE, PERF_COUNT_HW_CPU_CYCLES | ((__u64)pmu->type << PERF_PMU_TYPE_SHIFT)))
+			return false;
+	}
+
+	return true;
+}
+
+static bool perf_pmus__do_support_extended_type;
+
+static void perf_pmus__init_supports_extended_type(void)
+{
+	perf_pmus__do_support_extended_type = __perf_pmus__supports_extended_type();
+}
+
 bool perf_pmus__supports_extended_type(void)
 {
-	return perf_pmus__num_core_pmus() > 1;
+	static pthread_once_t extended_type_once = PTHREAD_ONCE_INIT;
+
+	pthread_once(&extended_type_once, perf_pmus__init_supports_extended_type);
+
+	return perf_pmus__do_support_extended_type;
 }
 
 struct perf_pmu *evsel__find_pmu(const struct evsel *evsel)