[PATCH v2] selftests/cgroup: add PSI pressure trigger and validation tests

[PATCH v2] selftests/cgroup: add PSI pressure trigger and validation tests

[Tao Cui]

From: Tao Cui <cuitao@kylinos.cn>

The cgroup selftests have no PSI coverage. Add test_psi.c: trigger
smoke tests (one per fd, IRQ full-only), cgroup.pressure toggle, and a
CPU-pressure trigger test using over-subscription. Skips when PSI is
disabled or a resource is absent.

Signed-off-by: Tao Cui <cuitao@kylinos.cn>
---
Changes since v1 (Michal Koutny, sashiko review):
- Trim errno checks to smoke level; loosen toggle range checks.
- Switch trigger test from memory to CPU pressure (deterministic, no SKIP).
- churn_memory() removed -- sysconf/shared-helper point is moot.
- Runner stays out of the cgroup; hogs reaped via cg_killall().
- Add PSI/IRQ skip-guards, zero-init buffers, .gitignore entry.
---
 tools/testing/selftests/cgroup/.gitignore |   1 +
 tools/testing/selftests/cgroup/Makefile   |   2 +
 tools/testing/selftests/cgroup/config     |   1 +
 tools/testing/selftests/cgroup/test_psi.c | 280 ++++++++++++++++++++++
 4 files changed, 284 insertions(+)
 create mode 100644 tools/testing/selftests/cgroup/test_psi.c

diff --git a/tools/testing/selftests/cgroup/.gitignore b/tools/testing/selftests/cgroup/.gitignore
index 952e4448bf07..ce2b907c57ea 100644
--- a/tools/testing/selftests/cgroup/.gitignore
+++ b/tools/testing/selftests/cgroup/.gitignore
@@ -8,5 +8,6 @@ test_kill
 test_kmem
 test_memcontrol
 test_pids
+test_psi
 test_zswap
 wait_inotify
diff --git a/tools/testing/selftests/cgroup/Makefile b/tools/testing/selftests/cgroup/Makefile
index e01584c2189a..a8c69e37332a 100644
--- a/tools/testing/selftests/cgroup/Makefile
+++ b/tools/testing/selftests/cgroup/Makefile
@@ -16,6 +16,7 @@ TEST_GEN_PROGS += test_kill
 TEST_GEN_PROGS += test_kmem
 TEST_GEN_PROGS += test_memcontrol
 TEST_GEN_PROGS += test_pids
+TEST_GEN_PROGS += test_psi
 TEST_GEN_PROGS += test_zswap
 
 LOCAL_HDRS += $(selfdir)/clone3/clone3_selftests.h $(selfdir)/pidfd/pidfd.h
@@ -32,4 +33,5 @@ $(OUTPUT)/test_kill: $(LIBCGROUP_O)
 $(OUTPUT)/test_kmem: $(LIBCGROUP_O)
 $(OUTPUT)/test_memcontrol: $(LIBCGROUP_O)
 $(OUTPUT)/test_pids: $(LIBCGROUP_O)
+$(OUTPUT)/test_psi: $(LIBCGROUP_O)
 $(OUTPUT)/test_zswap: $(LIBCGROUP_O)
diff --git a/tools/testing/selftests/cgroup/config b/tools/testing/selftests/cgroup/config
index 39f979690dd3..8a3ef479e83d 100644
--- a/tools/testing/selftests/cgroup/config
+++ b/tools/testing/selftests/cgroup/config
@@ -4,3 +4,4 @@ CONFIG_CGROUP_FREEZER=y
 CONFIG_CGROUP_SCHED=y
 CONFIG_MEMCG=y
 CONFIG_PAGE_COUNTER=y
+CONFIG_PSI=y
diff --git a/tools/testing/selftests/cgroup/test_psi.c b/tools/testing/selftests/cgroup/test_psi.c
new file mode 100644
index 000000000000..51dc35e26013
--- /dev/null
+++ b/tools/testing/selftests/cgroup/test_psi.c
@@ -0,0 +1,280 @@
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <poll.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include <linux/limits.h>
+
+#include "kselftest.h"
+#include "cgroup_util.h"
+
+/* How long to wait for the CPU-pressure trigger before giving up. */
+#define PSI_POLL_TIMEOUT_MS	5000
+
+static int pressure_open(const char *resource)
+{
+	char path[PATH_MAX];
+
+	snprintf(path, sizeof(path), "/proc/pressure/%s", resource);
+	return open(path, O_RDWR);
+}
+
+/* Write a trigger descriptor, including the trailing NUL the parser expects. */
+static ssize_t write_trigger(int fd, const char *trigger)
+{
+	return write(fd, trigger, strlen(trigger) + 1);
+}
+
+/* Trigger smoke test: second on same fd -> EBUSY; IRQ rejects "some". */
+static int test_proc_triggers(const char *root)
+{
+	static const char *const resources[] = { "io", "memory", "cpu" };
+	int ret = KSFT_FAIL;
+	int fd = -1;
+	int i;
+
+	(void)root;
+
+	for (i = 0; i < (int)ARRAY_SIZE(resources); i++) {
+		fd = pressure_open(resources[i]);
+		if (fd < 0) {
+			ksft_print_msg("open /proc/pressure/%s: %s\n",
+				       resources[i], strerror(errno));
+			goto cleanup;
+		}
+
+		errno = 0;
+		if (write_trigger(fd, "some 150000 2000000") <= 0) {
+			ksft_print_msg("%s: 'some' trigger rejected: %s\n",
+				       resources[i], strerror(errno));
+			goto cleanup;
+		}
+		/* A second trigger on the same fd must fail with EBUSY. */
+		errno = 0;
+		if (write_trigger(fd, "full 150000 2000000") != -1 || errno != EBUSY) {
+			ksft_print_msg("%s: second trigger expected EBUSY, got %s\n",
+				       resources[i], strerror(errno));
+			goto cleanup;
+		}
+
+		close(fd);
+		fd = -1;
+	}
+
+	/* IRQ is full-only, and only exists with CONFIG_IRQ_TIME_ACCOUNTING. */
+	fd = pressure_open("irq");
+	if (fd >= 0) {
+		errno = 0;
+		if (write_trigger(fd, "some 150000 1000000") != -1) {
+			ksft_print_msg("irq 'some': expected failure, got %s\n",
+				       strerror(errno));
+			goto cleanup;
+		}
+		close(fd);
+		fd = -1;
+	}
+
+	ret = KSFT_PASS;
+cleanup:
+	if (fd >= 0)
+		close(fd);
+	return ret;
+}
+
+/* cgroup.pressure 0/1 hides/shows the *.pressure files and round-trips. */
+static int test_cgroup_pressure_toggle(const char *root)
+{
+	char buf[BUF_SIZE] = { 0 };
+	char *cg = NULL;
+	int ret = KSFT_FAIL;
+
+	cg = cg_name(root, "psi_toggle_test");
+	if (!cg)
+		goto cleanup;
+	if (cg_create(cg))
+		goto cleanup;
+
+	if (cg_write(cg, "cgroup.pressure", "0")) {
+		ksft_print_msg("failed to disable cgroup.pressure\n");
+		goto cleanup;
+	}
+	if (cg_read(cg, "cgroup.pressure", buf, sizeof(buf)) < 0 || atoi(buf) != 0) {
+		ksft_print_msg("cgroup.pressure=0 readback: '%s'\n", buf);
+		goto cleanup;
+	}
+	if (cg_read(cg, "memory.pressure", buf, sizeof(buf)) >= 0) {
+		ksft_print_msg("memory.pressure visible while disabled\n");
+		goto cleanup;
+	}
+
+	if (cg_write(cg, "cgroup.pressure", "1")) {
+		ksft_print_msg("failed to re-enable cgroup.pressure\n");
+		goto cleanup;
+	}
+	if (cg_read(cg, "cgroup.pressure", buf, sizeof(buf)) < 0 || atoi(buf) != 1) {
+		ksft_print_msg("cgroup.pressure=1 readback: '%s'\n", buf);
+		goto cleanup;
+	}
+	if (cg_read(cg, "memory.pressure", buf, sizeof(buf)) < 0) {
+		ksft_print_msg("memory.pressure unreadable while enabled\n");
+		goto cleanup;
+	}
+
+	ret = KSFT_PASS;
+cleanup:
+	if (cg)
+		cg_destroy(cg);
+	free(cg);
+	return ret;
+}
+
+/* Induce deterministic CPU pressure (more hogs than CPUs). */
+static int test_cgroup_trigger_fire(const char *root)
+{
+	char *cg = NULL, *cpupress = NULL;
+	int fd = -1, ret = KSFT_FAIL;
+	struct pollfd pfd;
+	long ncpus, i;
+	pid_t pid;
+
+	cg = cg_name(root, "psi_trigger_test");
+	if (!cg)
+		goto cleanup;
+	if (cg_create(cg))
+		goto cleanup;
+
+	cpupress = cg_control(cg, "cpu.pressure");
+	if (!cpupress)
+		goto cleanup;
+	fd = open(cpupress, O_RDWR);
+	if (fd < 0) {
+		ksft_print_msg("open cpu.pressure: %s\n", strerror(errno));
+		goto cleanup;
+	}
+
+	/* 1us threshold in a 1s window: any cpu stall fires it. */
+	errno = 0;
+	if (write_trigger(fd, "some 1 1000000") <= 0) {
+		ksft_print_msg("arming trigger failed: %s\n", strerror(errno));
+		goto cleanup;
+	}
+
+	ncpus = sysconf(_SC_NPROCESSORS_ONLN);
+	if (ncpus <= 0)
+		ncpus = 1;
+
+	pid = fork();
+	if (pid < 0) {
+		ksft_print_msg("fork: %s\n", strerror(errno));
+		goto cleanup;
+	}
+	if (pid == 0) {
+		/* Enter the cgroup, then over-subscribe it with CPU hogs. */
+		if (cg_enter_current(cg))
+			_exit(KSFT_FAIL);
+		for (i = 0; i < ncpus; i++) {
+			if (fork() == 0) {
+				for (;;)
+					asm volatile("" ::: "memory");
+				_exit(0);
+			}
+		}
+		for (;;)
+			asm volatile("" ::: "memory");	/* child is also a hog */
+		_exit(0);
+	}
+
+	pfd.fd = fd;
+	pfd.events = POLLPRI;
+	switch (poll(&pfd, 1, PSI_POLL_TIMEOUT_MS)) {
+	case -1:
+		ksft_print_msg("poll: %s\n", strerror(errno));
+		break;
+	case 0:
+		ksft_print_msg("no trigger event; could not induce cpu pressure\n");
+		ret = KSFT_SKIP;
+		break;
+	default:
+		if (pfd.revents & POLLPRI)
+			ret = KSFT_PASS;
+		else
+			ksft_print_msg("poll returned 0x%x\n", pfd.revents);
+		break;
+	}
+
+	/* Stop the hogs (bounded, so waitpid can't hang) and reap the child. */
+	cg_killall(cg);
+	waitpid(pid, NULL, 0);
+
+cleanup:
+	if (fd >= 0)
+		close(fd);
+	if (cg) {
+		cg_killall(cg);
+		cg_destroy(cg);
+	}
+	free(cpupress);
+	free(cg);
+	return ret;
+}
+
+#define TEST(x) { #x, x }
+
+struct psi_test {
+	const char *name;
+	int (*fn)(const char *root);
+};
+
+static struct psi_test tests[] = {
+	TEST(test_proc_triggers),
+	TEST(test_cgroup_pressure_toggle),
+	TEST(test_cgroup_trigger_fire),
+};
+
+int main(int argc, char **argv)
+{
+	char root[PATH_MAX];
+	int mempress_fd;
+	int i;
+
+	(void)argc;
+
+	ksft_print_header();
+	ksft_set_plan(ARRAY_SIZE(tests));
+
+	if (cg_find_unified_root(root, sizeof(root), NULL))
+		ksft_exit_skip("cgroup v2 isn't mounted\n");
+
+	/* PSI must be enabled (CONFIG_PSI=y, not default-disabled). */
+	mempress_fd = open("/proc/pressure/memory", O_RDONLY);
+	if (mempress_fd < 0)
+		ksft_exit_skip("PSI unavailable (CONFIG_PSI=n or psi=0)\n");
+	close(mempress_fd);
+
+	if (cg_read_strstr(root, "cgroup.controllers", "memory"))
+		ksft_exit_skip("memory controller isn't available\n");
+	if (cg_read_strstr(root, "cgroup.subtree_control", "memory"))
+		if (cg_write(root, "cgroup.subtree_control", "+memory"))
+			ksft_exit_skip("failed to enable memory controller\n");
+
+	for (i = 0; i < (int)ARRAY_SIZE(tests); i++) {
+		switch (tests[i].fn(root)) {
+		case KSFT_PASS:
+			ksft_test_result_pass("%s\n", tests[i].name);
+			break;
+		case KSFT_SKIP:
+			ksft_test_result_skip("%s\n", tests[i].name);
+			break;
+		default:
+			ksft_test_result_fail("%s\n", tests[i].name);
+			break;
+		}
+	}
+
+	ksft_finished();
+}
-- 
2.43.0

Re: [PATCH v2] selftests/cgroup: add PSI pressure trigger and validation tests

[Michal Koutný]

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Hi,
thanks for continuing with this.

On Tue, Jul 28, 2026 at 04:37:42PM +0800, Tao Cui <cui.tao@linux.dev> wrote:
> +/* Trigger smoke test: second on same fd -> EBUSY; IRQ rejects "some". */
> +static int test_proc_triggers(const char *root)
> +{
> +	static const char *const resources[] = { "io", "memory", "cpu" };
> +	int ret = KSFT_FAIL;
> +	int fd = -1;
> +	int i;
> +
> +	(void)root;

WTH?

> +
> +	for (i = 0; i < (int)ARRAY_SIZE(resources); i++) {

This (int) cast is quite uncommon, look around.

> +/* Induce deterministic CPU pressure (more hogs than CPUs). */
> +static int test_cgroup_trigger_fire(const char *root)
> +{
> +	char *cg = NULL, *cpupress = NULL;
> +	int fd = -1, ret = KSFT_FAIL;
> +	struct pollfd pfd;
> +	long ncpus, i;
> +	pid_t pid;
> +
> +	cg = cg_name(root, "psi_trigger_test");
> +	if (!cg)
> +		goto cleanup;
> +	if (cg_create(cg))
> +		goto cleanup;
> +
> +	cpupress = cg_control(cg, "cpu.pressure");
> +	if (!cpupress)
> +		goto cleanup;
> +	fd = open(cpupress, O_RDWR);
> +	if (fd < 0) {
> +		ksft_print_msg("open cpu.pressure: %s\n", strerror(errno));
> +		goto cleanup;
> +	}
> +
> +	/* 1us threshold in a 1s window: any cpu stall fires it. */
> +	errno = 0;
> +	if (write_trigger(fd, "some 1 1000000") <= 0) {
> +		ksft_print_msg("arming trigger failed: %s\n", strerror(errno));
> +		goto cleanup;
> +	}

When I see this, could you increase the window size to 2000000 (so that
it has potential to run for unprivileged users)?

> +
> +	ncpus = sysconf(_SC_NPROCESSORS_ONLN);
> +	if (ncpus <= 0)
> +		ncpus = 1;
> +
> +	pid = fork();
> +	if (pid < 0) {
> +		ksft_print_msg("fork: %s\n", strerror(errno));
> +		goto cleanup;
> +	}
> +	if (pid == 0) {
> +		/* Enter the cgroup, then over-subscribe it with CPU hogs. */
> +		if (cg_enter_current(cg))
> +			_exit(KSFT_FAIL);
> +		for (i = 0; i < ncpus; i++) {
> +			if (fork() == 0) {
> +				for (;;)
> +					asm volatile("" ::: "memory");
> +				_exit(0);
> +			}
> +		}
> +		for (;;)
> +			asm volatile("" ::: "memory");	/* child is also a hog */
> +		_exit(0);
> +	}

This part could be replaced with generalized hog_cpus_timed() from
test_cpu.c (after move to cgroup_util.c).

> +int main(int argc, char **argv)
> +{
> +	char root[PATH_MAX];
> +	int mempress_fd;
> +	int i;
> +
> +	(void)argc;

What's up with this?

> +
> +	ksft_print_header();
> +	ksft_set_plan(ARRAY_SIZE(tests));
> +
> +	if (cg_find_unified_root(root, sizeof(root), NULL))
> +		ksft_exit_skip("cgroup v2 isn't mounted\n");
> +
> +	/* PSI must be enabled (CONFIG_PSI=y, not default-disabled). */
> +	mempress_fd = open("/proc/pressure/memory", O_RDONLY);
> +	if (mempress_fd < 0)
> +		ksft_exit_skip("PSI unavailable (CONFIG_PSI=n or psi=0)\n");
> +	close(mempress_fd);
> +
> +	if (cg_read_strstr(root, "cgroup.controllers", "memory"))
> +		ksft_exit_skip("memory controller isn't available\n");
> +	if (cg_read_strstr(root, "cgroup.subtree_control", "memory"))
> +		if (cg_write(root, "cgroup.subtree_control", "+memory"))
> +			ksft_exit_skip("failed to enable memory controller\n");

The memory controller is unnecessary now, right?


Regards,
Michal

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Re: [PATCH v2] selftests/cgroup: add PSI pressure trigger and validation tests

[Suren Baghdasaryan]

On Thu, Aug 6, 2026 at 9:52 AM Michal Koutný <mkoutny@suse.com> wrote:
>
> Hi,
> thanks for continuing with this.

Thanks for adding these tests and sorry I was not able to review them
yet. I'll try to review them this weekend and will provide my
feedback.
Thanks,
Suren.

>
> On Tue, Jul 28, 2026 at 04:37:42PM +0800, Tao Cui <cui.tao@linux.dev> wrote:
> > +/* Trigger smoke test: second on same fd -> EBUSY; IRQ rejects "some". */
> > +static int test_proc_triggers(const char *root)
> > +{
> > +     static const char *const resources[] = { "io", "memory", "cpu" };
> > +     int ret = KSFT_FAIL;
> > +     int fd = -1;
> > +     int i;
> > +
> > +     (void)root;
>
> WTH?
>
> > +
> > +     for (i = 0; i < (int)ARRAY_SIZE(resources); i++) {
>
> This (int) cast is quite uncommon, look around.
>
> > +/* Induce deterministic CPU pressure (more hogs than CPUs). */
> > +static int test_cgroup_trigger_fire(const char *root)
> > +{
> > +     char *cg = NULL, *cpupress = NULL;
> > +     int fd = -1, ret = KSFT_FAIL;
> > +     struct pollfd pfd;
> > +     long ncpus, i;
> > +     pid_t pid;
> > +
> > +     cg = cg_name(root, "psi_trigger_test");
> > +     if (!cg)
> > +             goto cleanup;
> > +     if (cg_create(cg))
> > +             goto cleanup;
> > +
> > +     cpupress = cg_control(cg, "cpu.pressure");
> > +     if (!cpupress)
> > +             goto cleanup;
> > +     fd = open(cpupress, O_RDWR);
> > +     if (fd < 0) {
> > +             ksft_print_msg("open cpu.pressure: %s\n", strerror(errno));
> > +             goto cleanup;
> > +     }
> > +
> > +     /* 1us threshold in a 1s window: any cpu stall fires it. */
> > +     errno = 0;
> > +     if (write_trigger(fd, "some 1 1000000") <= 0) {
> > +             ksft_print_msg("arming trigger failed: %s\n", strerror(errno));
> > +             goto cleanup;
> > +     }
>
> When I see this, could you increase the window size to 2000000 (so that
> it has potential to run for unprivileged users)?
>
> > +
> > +     ncpus = sysconf(_SC_NPROCESSORS_ONLN);
> > +     if (ncpus <= 0)
> > +             ncpus = 1;
> > +
> > +     pid = fork();
> > +     if (pid < 0) {
> > +             ksft_print_msg("fork: %s\n", strerror(errno));
> > +             goto cleanup;
> > +     }
> > +     if (pid == 0) {
> > +             /* Enter the cgroup, then over-subscribe it with CPU hogs. */
> > +             if (cg_enter_current(cg))
> > +                     _exit(KSFT_FAIL);
> > +             for (i = 0; i < ncpus; i++) {
> > +                     if (fork() == 0) {
> > +                             for (;;)
> > +                                     asm volatile("" ::: "memory");
> > +                             _exit(0);
> > +                     }
> > +             }
> > +             for (;;)
> > +                     asm volatile("" ::: "memory");  /* child is also a hog */
> > +             _exit(0);
> > +     }
>
> This part could be replaced with generalized hog_cpus_timed() from
> test_cpu.c (after move to cgroup_util.c).
>
> > +int main(int argc, char **argv)
> > +{
> > +     char root[PATH_MAX];
> > +     int mempress_fd;
> > +     int i;
> > +
> > +     (void)argc;
>
> What's up with this?
>
> > +
> > +     ksft_print_header();
> > +     ksft_set_plan(ARRAY_SIZE(tests));
> > +
> > +     if (cg_find_unified_root(root, sizeof(root), NULL))
> > +             ksft_exit_skip("cgroup v2 isn't mounted\n");
> > +
> > +     /* PSI must be enabled (CONFIG_PSI=y, not default-disabled). */
> > +     mempress_fd = open("/proc/pressure/memory", O_RDONLY);
> > +     if (mempress_fd < 0)
> > +             ksft_exit_skip("PSI unavailable (CONFIG_PSI=n or psi=0)\n");
> > +     close(mempress_fd);
> > +
> > +     if (cg_read_strstr(root, "cgroup.controllers", "memory"))
> > +             ksft_exit_skip("memory controller isn't available\n");
> > +     if (cg_read_strstr(root, "cgroup.subtree_control", "memory"))
> > +             if (cg_write(root, "cgroup.subtree_control", "+memory"))
> > +                     ksft_exit_skip("failed to enable memory controller\n");
>
> The memory controller is unnecessary now, right?
>
>
> Regards,
> Michal