linux-kernel - [PATCH 5/5] perf/dummy_pmu: Track and disable active events

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Message-ID: <20241008183501.1354695-6-lucas.demarchi@intel.com>
Date: Tue,  8 Oct 2024 13:35:01 -0500
From: Lucas De Marchi <lucas.demarchi@...el.com>
To: linux-kernel@...r.kernel.org
Cc: dri-devel@...ts.freedesktop.org,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Umesh Nerlige Ramappa <umesh.nerlige.ramappa@...el.com>,
	Ian Rogers <irogers@...gle.com>,
	Tvrtko Ursulin <tvrtko.ursulin@...lia.com>,
	Lucas De Marchi <lucas.demarchi@...el.com>
Subject: [PATCH 5/5] perf/dummy_pmu: Track and disable active events

When unregistering the PMU, disable the currently active events. This
allows userspace to see the change and possibly reacting on it, like
reopening the fd. With perf-stat, "<not counted>" starts to be printed:

	$ stat -e dummy_pmu_0/test-event-1/ -I1000
	1.001227905                 12      dummy_pmu_0/test-event-1/
	2.004009349                 11      dummy_pmu_0/test-event-1/
	3.005785067                  0      dummy_pmu_0/test-event-1/
	4.008565935      <not counted>      dummy_pmu_0/test-event-1/
	5.010446891      <not counted>      dummy_pmu_0/test-event-1/

Signed-off-by: Lucas De Marchi <lucas.demarchi@...el.com>
---
 kernel/events/dummy_pmu.c | 40 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/kernel/events/dummy_pmu.c b/kernel/events/dummy_pmu.c
index c07e111bff01..496cb8469a05 100644
--- a/kernel/events/dummy_pmu.c
+++ b/kernel/events/dummy_pmu.c
@@ -14,6 +14,7 @@
 #include <linux/random.h>
 #include <linux/seq_file.h>
 #include <linux/types.h>
+#include <linux/xarray.h>
 
 struct dummy_mod {
 	struct dentry *debugfs_root;
@@ -25,6 +26,7 @@ struct dummy_mod {
 struct dummy_pmu {
 	struct pmu base;
 	char *name;
+	struct xarray active_events;
 	bool registered;
 };
 
@@ -97,9 +99,25 @@ static const struct attribute_group *attr_groups[] = {
 	NULL,
 };
 
+static void dummy_pmu_event_destroy(struct perf_event *event)
+{
+	struct dummy_pmu *pmu = event_to_pmu(event);
+	unsigned long idx;
+	struct perf_event *e;
+
+	/* Event not active anymore */
+	xa_for_each(&pmu->active_events, idx, e)
+		if (e == event) {
+			xa_erase(&pmu->active_events, idx);
+			break;
+		}
+}
+
 static int dummy_pmu_event_init(struct perf_event *event)
 {
 	struct dummy_pmu *pmu = event_to_pmu(event);
+	u32 event_id;
+	int ret;
 
 	if (!pmu->registered)
 		return -ENODEV;
@@ -117,6 +135,13 @@ static int dummy_pmu_event_init(struct perf_event *event)
 	if (event->cpu < 0)
 		return -EINVAL;
 
+	ret = xa_alloc(&pmu->active_events, &event_id, event,
+			xa_limit_32b, GFP_KERNEL);
+	if (ret)
+		return ret;
+
+	event->destroy = dummy_pmu_event_destroy;
+
 	return 0;
 }
 
@@ -232,6 +257,8 @@ static int device_init(struct dummy_device *d)
 	if (ret)
 		goto fail;
 
+	xa_init_flags(&d->pmu.active_events, XA_FLAGS_ALLOC);
+
 	d->pmu.registered = true;
 	pr_info("Device registered: %s\n", d->pmu.name);
 
@@ -248,9 +275,22 @@ static int device_init(struct dummy_device *d)
 	return ret;
 }
 
+static void disable_active_events(struct dummy_pmu *pmu)
+{
+	struct perf_event *event;
+	unsigned long idx;
+
+	xa_for_each(&pmu->active_events, idx, event) {
+		xa_erase(&pmu->active_events, idx);
+		perf_event_disable(event);
+	}
+}
+
 static void device_exit(struct dummy_device *d)
 {
 	d->pmu.registered = false;
+
+	disable_active_events(&d->pmu);
 	perf_pmu_unregister(&d->pmu.base);
 
 	pr_info("Device released: %s\n", d->pmu.name);
-- 
2.46.2