diff --git a/lib/igt_sysfs.c b/lib/igt_sysfs.c
index 6aafe5349..e734143ba 100644
--- a/lib/igt_sysfs.c
+++ b/lib/igt_sysfs.c
@@ -378,6 +378,42 @@ uint32_t igt_sysfs_get_u32(int dir, const char *attr)
 	return result;
 }
 
+/**
+ * igt_sysfs_get_u64:
+ * @dir: directory for the device from igt_sysfs_open()
+ * @attr: name of the sysfs node to open
+ *
+ * Convenience wrapper to read a unsigned 64bit integer from a sysfs file.
+ *
+ * Returns:
+ * The value read.
+ */
+uint64_t igt_sysfs_get_u64(int dir, const char *attr)
+{
+	uint64_t result;
+
+	if (igt_sysfs_scanf(dir, attr, "%"PRIu64, &result) != 1)
+		return 0;
+
+	return result;
+}
+
+/**
+ * igt_sysfs_set_u64:
+ * @dir: directory for the device from igt_sysfs_open()
+ * @attr: name of the sysfs node to open
+ * @value: value to set
+ *
+ * Convenience wrapper to write a unsigned 64bit integer to a sysfs file.
+ *
+ * Returns:
+ * True if successfully written
+ */
+bool igt_sysfs_set_u64(int dir, const char *attr, uint64_t value)
+{
+	return igt_sysfs_printf(dir, attr, "%"PRIu64, value) > 0;
+}
+
 /**
  * igt_sysfs_set_u32:
  * @dir: directory for the device from igt_sysfs_open()
diff --git a/lib/igt_sysfs.h b/lib/igt_sysfs.h
index 64935a5ca..56741a0a3 100644
--- a/lib/igt_sysfs.h
+++ b/lib/igt_sysfs.h
@@ -47,6 +47,9 @@ int igt_sysfs_printf(int dir, const char *attr, const char *fmt, ...)
 uint32_t igt_sysfs_get_u32(int dir, const char *attr);
 bool igt_sysfs_set_u32(int dir, const char *attr, uint32_t value);
 
+uint64_t igt_sysfs_get_u64(int dir, const char *attr);
+bool igt_sysfs_set_u64(int dir, const char *attr, uint64_t value);
+
 bool igt_sysfs_get_boolean(int dir, const char *attr);
 bool igt_sysfs_set_boolean(int dir, const char *attr, bool value);
 
diff --git a/tests/Makefile.sources b/tests/Makefile.sources
index 1c227e750..3f663fe7e 100644
--- a/tests/Makefile.sources
+++ b/tests/Makefile.sources
@@ -114,6 +114,9 @@ TESTS_progs = \
 TESTS_progs += api_intel_bb
 api_intel_bb_SOURCES = i915/api_intel_bb.c
 
+TESTS_progs += sysfs_clients
+sysfs_clients_SOURCES = i915/sysfs_clients.c
+
 TESTS_progs += sysfs_defaults
 sysfs_defaults_SOURCES = i915/sysfs_defaults.c
 
diff --git a/tests/i915/sysfs_clients.c b/tests/i915/sysfs_clients.c
new file mode 100644
index 000000000..3a5c4cedf
--- /dev/null
+++ b/tests/i915/sysfs_clients.c
@@ -0,0 +1,361 @@
+/* SPDX-License-Identifier: MIT */
+/*
+ * Copyright © 2021 Intel Corporation
+ */
+
+#include <ctype.h>
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <inttypes.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "drmtest.h"
+#include "i915/gem.h"
+#include "i915/gem_context.h"
+#include "i915/gem_engine_topology.h"
+#include "igt_aux.h"
+#include "igt_dummyload.h"
+#include "igt_sysfs.h"
+#include "ioctl_wrappers.h"
+
+static void pidname(int i915, int clients)
+{
+	struct dirent *de;
+	int sv[2], rv[2];
+	char buf[280];
+	int me = -1;
+	long count;
+	pid_t pid;
+	DIR *dir;
+	int len;
+
+	dir = fdopendir(dup(clients));
+	igt_assert(dir);
+	rewinddir(dir);
+
+	count = 0;
+	while ((de = readdir(dir))) {
+		if (!isdigit(de->d_name[0]))
+			continue;
+
+		snprintf(buf, sizeof(buf), "%s/name", de->d_name);
+		len = igt_sysfs_read(clients, buf, buf, sizeof(buf));
+		igt_assert_f(len > 0, "failed to open '%s/name'\n", de->d_name);
+		buf[len - 1] = '\0';
+		igt_debug("%s: %s\n", de->d_name, buf);
+
+		/* Ignore closed clients created by drm_driver_open() */
+		if (*buf == '<')
+			continue;
+
+		close(me);
+		me = openat(clients, de->d_name, O_DIRECTORY | O_RDONLY);
+		count++;
+	}
+	closedir(dir);
+
+	/* We expect there to be only the single client (us) running */
+	igt_assert_eq(count, 1);
+	igt_assert(me >= 0);
+
+	len = igt_sysfs_read(me, "name", buf, sizeof(buf));
+	igt_assert(len > 0);
+	buf[len - 1] = '\0';
+
+	igt_info("My name: %s\n", buf);
+	igt_assert(strcmp(buf, igt_test_name()) == 0);
+
+	igt_assert(pipe(sv) == 0);
+	igt_assert(pipe(rv) == 0);
+
+	/* If give our fd to someone else, they take over ownership of client */
+	igt_fork(child, 1) {
+		read(sv[0], &pid, sizeof(pid));
+
+		gem_context_destroy(i915, gem_context_create(i915));
+
+		pid = getpid();
+		write(rv[1], &pid, sizeof(pid));
+	}
+	close(sv[0]);
+	close(rv[1]);
+
+	/* Child exists, but not yet running, we still own the client */
+	len = igt_sysfs_read(me, "pid", buf, sizeof(buf));
+	igt_assert(len > 0);
+	buf[len - 1] = '\0';
+
+	pid = getpid();
+	igt_info("My pid: %s\n", buf);
+	igt_assert_eq(atoi(buf), pid);
+
+	/* Release and wait for the child */
+	igt_assert_eq(write(sv[1], &pid, sizeof(pid)), sizeof(pid));
+	igt_assert_eq(read(rv[0], &pid, sizeof(pid)), sizeof(pid));
+
+	/* Now child owns the client and pid should be updated to match */
+	len = igt_sysfs_read(me, "pid", buf, sizeof(buf));
+	igt_assert(len > 0);
+	buf[len - 1] = '\0';
+
+	igt_info("New pid: %s\n", buf);
+	igt_assert_eq(atoi(buf), pid);
+	igt_waitchildren();
+
+	/* Child has definitely gone, but the client should remain */
+	len = igt_sysfs_read(me, "pid", buf, sizeof(buf));
+	igt_assert(len > 0);
+	buf[len - 1] = '\0';
+
+	igt_info("Old pid: %s\n", buf);
+	igt_assert_eq(atoi(buf), pid);
+
+	close(sv[1]);
+	close(rv[0]);
+	close(me);
+}
+
+static long count_clients(int clients)
+{
+	struct dirent *de;
+	long count = 0;
+	char buf[280];
+	DIR *dir;
+
+	dir = fdopendir(dup(clients));
+	igt_assert(dir);
+	rewinddir(dir);
+
+	while ((de = readdir(dir))) {
+		int len;
+
+		if (!isdigit(de->d_name[0]))
+			continue;
+
+		snprintf(buf, sizeof(buf), "%s/name", de->d_name);
+		len = igt_sysfs_read(clients, buf, buf, sizeof(buf));
+		if (len < 0)
+			continue;
+
+		count += *buf != '<';
+	}
+	closedir(dir);
+
+	return count;
+}
+
+static void create(int i915, int clients)
+{
+	int fd[16];
+
+	/* Each new open("/dev/dri/cardN") is a new client */
+	igt_assert_eq(count_clients(clients), 1);
+	for (int i = 0; i < ARRAY_SIZE(fd); i++) {
+		fd[i] = gem_reopen_driver(i915);
+		igt_assert_eq(count_clients(clients), i + 2);
+	}
+
+	for (int i = 0; i < ARRAY_SIZE(fd); i++)
+		close(fd[i]);
+
+	/* Cleanup delayed behind rcu */
+	igt_until_timeout(30) {
+		usleep(0);
+		if (count_clients(clients) == 1)
+			break;
+		usleep(10000);
+	}
+	igt_assert_eq(count_clients(clients), 1);
+}
+
+static int find_me(int clients, pid_t pid)
+{
+	struct dirent *de;
+	char buf[280];
+	int me = -1;
+	DIR *dir;
+
+	dir = fdopendir(dup(clients));
+	igt_assert(dir);
+	rewinddir(dir);
+
+	while ((de = readdir(dir))) {
+		int ret;
+
+		if (!isdigit(de->d_name[0]))
+			continue;
+
+		snprintf(buf, sizeof(buf), "%s/pid", de->d_name);
+		ret = igt_sysfs_read(clients, buf, buf, sizeof(buf));
+		igt_assert_f(ret > 0, "failed to open '%s/pid'\n", de->d_name);
+		if (atoi(buf) != pid)
+			continue;
+
+		me = openat(clients, de->d_name, O_DIRECTORY | O_RDONLY);
+		break;
+	}
+
+	closedir(dir);
+	return me;
+}
+
+#define MAX_CLASS 64
+static int read_runtime(int client, uint64_t *runtime)
+{
+	int fd = openat(client, "busy", O_DIRECTORY | O_RDONLY);
+	DIR *dir = fdopendir(fd);
+	struct dirent *de;
+	int count = 0;
+
+	memset(runtime, 0, sizeof(*runtime) * MAX_CLASS);
+	while ((de = readdir(dir))) {
+		int class;
+
+		if (!isdigit(de->d_name[0]))
+			continue;
+
+		class = atoi(de->d_name);
+		igt_assert(class < MAX_CLASS);
+		runtime[class] = igt_sysfs_get_u64(fd, de->d_name);
+
+		count += runtime[class] != 0;
+	}
+	closedir(dir);
+
+	return count;
+}
+
+static uint64_t measured_usleep(unsigned int usec)
+{
+	struct timespec tv;
+	unsigned int slept;
+
+	slept = igt_nsec_elapsed(memset(&tv, 0, sizeof(tv)));
+	igt_assert(slept == 0);
+	do {
+		usleep(usec - slept);
+		slept = igt_nsec_elapsed(&tv) / 1000;
+	} while (slept < usec);
+
+	return igt_nsec_elapsed(&tv);
+}
+
+static void busy(int i915, int clients)
+{
+	const struct intel_execution_engine2 *e;
+	uint64_t active[MAX_CLASS];
+	uint64_t idle[MAX_CLASS];
+	uint64_t old[MAX_CLASS];
+	uint64_t classes = 0;
+	int expect = 0;
+	int64_t delay;
+	igt_spin_t *spin;
+	int me;
+
+	/* Create a fresh client with 0 runtime */
+	i915 = gem_reopen_driver(i915);
+
+	me = find_me(clients, getpid());
+	igt_assert(me != -1);
+	igt_require(faccessat(me, "busy", 0, F_OK) == 0);
+
+	spin = igt_spin_new(i915,
+			    gem_context_create(i915),
+			    .flags = IGT_SPIN_POLL_RUN);
+	__for_each_physical_engine(i915, e) {
+		spin->execbuf.flags &= ~63;
+		spin->execbuf.flags |= e->flags;
+		gem_execbuf(i915, &spin->execbuf);
+
+		if (!(classes & (1ull << e->class)))
+			expect++;
+		classes |= 1ull << e->class;
+	}
+	igt_spin_busywait_until_started(spin);
+
+	delay = -500000; /* 500us slack */
+	memset(old, 0, sizeof(old));
+	for (int pass = 0; pass < 5; pass++) {
+		delay += measured_usleep(1000);
+		igt_debug("delay: %'"PRIu64"ns\n", delay);
+
+		/* Check that we accumulate the runtime, while active */
+		igt_assert_eq(read_runtime(me, active), expect);
+		for (int i = 0; i < ARRAY_SIZE(active); i++) {
+			if (!active[i])
+				continue;
+
+			igt_info("active[%d]: %'"PRIu64"ns\n", i, active[i]);
+			igt_assert(active[i] > old[i]); /* monotonic */
+			igt_assert(active[i] > delay); /* within reason */
+		}
+	}
+
+	gem_quiescent_gpu(i915);
+
+	/* And again now idle */
+	igt_assert_eq(read_runtime(me, idle), expect);
+	for (int i = 0; i < ARRAY_SIZE(idle); i++) {
+		if (!idle[i])
+			continue;
+
+		igt_info("idle[%d]: %'"PRIu64"ns\n", i, idle[i]);
+		igt_assert(idle[i] >= active[i]);
+	}
+
+	gem_context_destroy(i915, spin->execbuf.rsvd1);
+	igt_spin_free(i915, spin);
+
+	/* And finally after the executing context is no more */
+	igt_assert_eq(read_runtime(me, old), expect);
+	for (int i = 0; i < ARRAY_SIZE(old); i++) {
+		if (!old[i])
+			continue;
+
+		igt_info("old[%d]: %'"PRIu64"ns\n", i, old[i]);
+		igt_assert_eq_u64(old[i], idle[i]);
+	}
+
+	close(i915);
+}
+
+igt_main
+{
+	int i915 = -1, clients = -1;
+
+	igt_fixture {
+		int sys;
+
+		/* Don't allow [too many] extra clients to be opened */
+		i915 = __drm_open_driver(DRIVER_INTEL);
+		igt_require_gem(i915);
+
+		sys = igt_sysfs_open(i915);
+		igt_require(sys != -1);
+
+		clients = openat(sys, "clients", O_RDONLY);
+		igt_require(clients != -1);
+
+		close(sys);
+	}
+
+	igt_subtest("pidname")
+		pidname(i915, clients);
+
+	igt_subtest("create")
+		create(i915, clients);
+
+	igt_subtest("busy") {
+		igt_fork(child, 1)
+			busy(i915, clients);
+		igt_waitchildren();
+	}
+
+	igt_fixture {
+		close(clients);
+		close(i915);
+	}
+}
diff --git a/tests/meson.build b/tests/meson.build
index ff924ff99..825e01833 100644
--- a/tests/meson.build
+++ b/tests/meson.build
@@ -236,6 +236,7 @@ i915_progs = [
 	'i915_query',
 	'i915_selftest',
 	'i915_suspend',
+	'sysfs_clients',
 	'sysfs_defaults',
 	'sysfs_heartbeat_interval',
 	'sysfs_preempt_timeout',
