[PATCH 2/4] perf record: Support sample-read topdown metric group

[kan . liang]

From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>

With the hardware TopDown metrics feature, sample-read feature should be
supported for a topdown group, e.g., sample a non-topdown event and read
a topdown metric group. But the current perf record code errors out.

For a topdown metric group, the slots event must be the leader of the
group, but the leader slots event doesn't support sampling.

To support sample-read the topdown metric group, use the 2nd event of
the group as the "leader" for the purposes of sampling.

Only the platform with Topdown metic feature supports sample-read the
topdown group. Add arch_topdown_sample_read() to indicate whether the
topdown group supports sample-read.

Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
---
 tools/perf/arch/x86/util/topdown.c | 35 ++++++++++++++++++++++++++++++
 tools/perf/util/record.c           |  3 ++-
 tools/perf/util/topdown.c          |  5 +++++
 tools/perf/util/topdown.h          |  2 ++
 4 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/tools/perf/arch/x86/util/topdown.c b/tools/perf/arch/x86/util/topdown.c
index 597e963fb3e7..fcf1f9c17a44 100644
--- a/tools/perf/arch/x86/util/topdown.c
+++ b/tools/perf/arch/x86/util/topdown.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <stdio.h>
 #include "api/fs/fs.h"
+#include "util/pmu.h"
 #include "util/topdown.h"
 
 /*
@@ -26,3 +27,37 @@ void arch_topdown_group_warn(void)
 		"nmi_watchdog enabled with topdown. May give wrong results.\n"
 		"Disable with echo 0 > /proc/sys/kernel/nmi_watchdog\n");
 }
+
+#define TOPDOWN_SLOTS		0x0400
+
+static bool is_topdown_slots_event(struct evsel *counter)
+{
+	if (!counter->pmu_name)
+		return false;
+
+	if (strcmp(counter->pmu_name, "cpu"))
+		return false;
+
+	if (counter->core.attr.config == TOPDOWN_SLOTS)
+		return true;
+
+	return false;
+}
+
+/*
+ * Check whether a topdown group supports sample-read.
+ *
+ * Only Topdown metic supports sample-read. The slots
+ * event must be the leader of the topdown group.
+ */
+
+bool arch_topdown_sample_read(struct evsel *leader)
+{
+	if (!pmu_have_event("cpu", "slots"))
+		return false;
+
+	if (is_topdown_slots_event(leader))
+		return true;
+
+	return false;
+}
diff --git a/tools/perf/util/record.c b/tools/perf/util/record.c
index a4cc11592f6b..a857a13b0544 100644
--- a/tools/perf/util/record.c
+++ b/tools/perf/util/record.c
@@ -13,6 +13,7 @@
 #include "util/perf_api_probe.h"
 #include "record.h"
 #include "../perf-sys.h"
+#include "topdown.h"
 
 /*
  * evsel__config_leader_sampling() uses special rules for leader sampling.
@@ -23,7 +24,7 @@ static struct evsel *evsel__read_sampler(struct evsel *evsel, struct evlist *evl
 {
 	struct evsel *leader = evsel->leader;
 
-	if (evsel__is_aux_event(leader)) {
+	if (evsel__is_aux_event(leader) || arch_topdown_sample_read(leader)) {
 		evlist__for_each_entry(evlist, evsel) {
 			if (evsel->leader == leader && evsel != evsel->leader)
 				return evsel;
diff --git a/tools/perf/util/topdown.c b/tools/perf/util/topdown.c
index a085b3c77c27..1081b20f9891 100644
--- a/tools/perf/util/topdown.c
+++ b/tools/perf/util/topdown.c
@@ -51,3 +51,8 @@ __weak bool arch_topdown_check_group(bool *warn)
 __weak void arch_topdown_group_warn(void)
 {
 }
+
+__weak bool arch_topdown_sample_read(struct evsel *leader __maybe_unused)
+{
+	return false;
+}
diff --git a/tools/perf/util/topdown.h b/tools/perf/util/topdown.h
index e3d70e95f4f1..2f0d0b887639 100644
--- a/tools/perf/util/topdown.h
+++ b/tools/perf/util/topdown.h
@@ -1,9 +1,11 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 #ifndef TOPDOWN_H
 #define TOPDOWN_H 1
+#include "evsel.h"
 
 bool arch_topdown_check_group(bool *warn);
 void arch_topdown_group_warn(void);
+bool arch_topdown_sample_read(struct evsel *leader);
 
 int topdown_filter_events(const char **attr, char **str, bool use_group);
 
-- 
2.17.1