linux-kernel - [PATCH] perf topdown: Correct leader selection with sample

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Date: Fri, 14 Jun 2024 21:39:08 +0000
From: Dapeng Mi <dapeng1.mi@...ux.intel.com>
To: Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Kan Liang <kan.liang@...ux.intel.com>
Cc: linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Dapeng Mi <dapeng1.mi@...el.com>,
	Dapeng Mi <dapeng1.mi@...ux.intel.com>
Subject: [PATCH] perf topdown: Correct leader selection with sample_read enabled

Addresses an issue where, in the absence of a topdown metrics event
within a sampling group, the slots event was incorrectly bypassed as
the sampling leader when sample_read was enabled.

perf record -e '{slots,branches}:S' -c 10000 -vv sleep 1

In this case, the slots event should be sampled as leader but the
branches event is sampled in fact like the verbose output shows.

perf_event_attr:
  type                             4 (cpu)
  size                             168
  config                           0x400 (slots)
  sample_type                      IP|TID|TIME|READ|CPU|IDENTIFIER
  read_format                      ID|GROUP|LOST
  disabled                         1
  sample_id_all                    1
  exclude_guest                    1
------------------------------------------------------------
sys_perf_event_open: pid -1  cpu 0  group_fd -1  flags 0x8 = 5
------------------------------------------------------------
perf_event_attr:
  type                             0 (PERF_TYPE_HARDWARE)
  size                             168
  config                           0x4 (PERF_COUNT_HW_BRANCH_INSTRUCTIONS)
  { sample_period, sample_freq }   10000
  sample_type                      IP|TID|TIME|READ|CPU|IDENTIFIER
  read_format                      ID|GROUP|LOST
  sample_id_all                    1
  exclude_guest                    1

The sample period of slots event instead of branches event is reset to
0.

This fix ensures the slots event remains the leader under these
conditions.

Reviewed-by: Kan Liang <kan.liang@...ux.intel.com>
Signed-off-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>
---
 tools/perf/arch/x86/util/topdown.c | 42 ++++++++++++++++++++++++++++--
 1 file changed, 40 insertions(+), 2 deletions(-)

diff --git a/tools/perf/arch/x86/util/topdown.c b/tools/perf/arch/x86/util/topdown.c
index 3f9a267d4501..aea6896bbb57 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 "api/fs/fs.h"
 #include "util/evsel.h"
+#include "util/evlist.h"
 #include "util/pmu.h"
 #include "util/pmus.h"
 #include "util/topdown.h"
@@ -31,6 +32,32 @@ bool topdown_sys_has_perf_metrics(void)
 	return has_perf_metrics;
 }
 
+static int perf_pmus__topdown_event(void *vstate, struct pmu_event_info *info)
+{
+	if (!strcmp(info->name, (char *)vstate))
+		return 1;
+
+	return 0;
+}
+
+static bool is_topdown_metric_event(struct evsel *event)
+{
+	struct perf_pmu *pmu;
+
+	if (!topdown_sys_has_perf_metrics())
+		return false;
+
+	if (event->core.attr.type != PERF_TYPE_RAW)
+		return false;
+
+	pmu = perf_pmus__find_by_type(PERF_TYPE_RAW);
+	if (pmu && perf_pmu__for_each_event(pmu, false, event->name,
+					    perf_pmus__topdown_event))
+		return true;
+
+	return false;
+}
+
 #define TOPDOWN_SLOTS		0x0400
 
 /*
@@ -41,11 +68,22 @@ bool topdown_sys_has_perf_metrics(void)
  */
 bool arch_topdown_sample_read(struct evsel *leader)
 {
+	struct evsel *event;
+
 	if (!evsel__sys_has_perf_metrics(leader))
 		return false;
 
-	if (leader->core.attr.config == TOPDOWN_SLOTS)
-		return true;
+	if (leader->core.attr.config != TOPDOWN_SLOTS)
+		return false;
+
+	/*
+	 * If slots event as leader event but no topdown metric events in group,
+	 * slots event should still sample as leader.
+	 */
+	evlist__for_each_entry(leader->evlist, event) {
+		if (event != leader && is_topdown_metric_event(event))
+			return true;
+	}
 
 	return false;
 }

base-commit: 92e5605a199efbaee59fb19e15d6cc2103a04ec2
-- 
2.40.1