On Mon, Aug 24, 2026 at 1:59 AM Tao Cui <[email protected]> wrote:
>
> From: Tao Cui <[email protected]>
>
> The cgroup selftests have no PSI coverage. Add test_psi.c: per-resource
> trigger smoke tests (one trigger per fd, IRQ full-only), a
> cgroup.pressure hide/show toggle test, and a CPU-pressure trigger test
> using over-subscription. Skips when PSI is disabled or a resource is
> absent.
>
> Signed-off-by: Tao Cui <[email protected]>
>
> ---
> Changes since v3 (Suren Baghdasaryan review):
> - Convert to the kselftest harness: each case is a TEST_F(psi, ...)
> with the cgroup root/PSI availability checks in FIXTURE_SETUP() and
> the teardown (kill hogs, destroy cgroup) in FIXTURE_TEARDOWN(),
> which also removes the "ret"/"created" bookkeeping.
> - A trigger that does not fire within the poll timeout is now a FAIL
> instead of a SKIP: ncpus+1 hogs with a 1usec threshold must stall,
> so a timeout indicates a real problem.
> - Treat a poll() timeout and a poll() error uniformly via ASSERT.
> - Check sysconf(_SC_NPROCESSORS_ONLN) only for -1 and report
> strerror(errno); declare variables one per line; for(;;) {}.
> - Make hog_cpu() die with the runner via PR_SET_PDEATHSIG so an
> interrupted run does not leave orphaned hogs pinning every CPU.
>
> Changes since v2 (Suren Baghdasaryan, Michal Koutny review):
> - Restructure the trigger test into per-resource cases (io, memory, cpu,
> irq) so a failure points at the specific resource; irq is skipped when
> /proc/pressure/irq is absent.
> - Spawn the CPU hogs with cg_run_nowait() instead of open-coding fork(),
> and arm the trigger with a 2s window so unprivileged users can set it.
> - Address the remaining review comments on cleanup and robustness:
> guard teardown with a "created" flag, use cg_read_strcmp() instead of
> atoi(), report strerror() on errors, and fix the unused-parameter and
> sign-compare nits.
>
> Changes since v1 (Michal Koutny, sashiko review):
> - Keep trigger tests smoke-level; switch the firing test from memory to
> CPU pressure; drop churn_memory().
> - Keep the runner out of the cgroup; add PSI/IRQ skip-guards and a
> .gitignore entry.
>
> v1: https://lore.kernel.org/all/[email protected]/
> v2: https://lore.kernel.org/all/[email protected]/
> v3: https://lore.kernel.org/all/[email protected]/
> ---
> 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 | 206 ++++++++++++++++++++++
> 4 files changed, 210 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..d5fab10f4fd4
> --- /dev/null
> +++ b/tools/testing/selftests/cgroup/test_psi.c
> @@ -0,0 +1,206 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define _GNU_SOURCE
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <poll.h>
> +#include <stdbool.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <unistd.h>
> +#include <sys/prctl.h>
> +#include <linux/limits.h>
> +
> +#include "../kselftest_harness.h"
> +#include "cgroup_util.h"
> +
> +#define PSI_POLL_TIMEOUT_MS 5000
> +
> +/* PSI triggers are written with a trailing NUL the kernel parser expects. */
> +static ssize_t write_trigger(int fd, const char *trigger)
> +{
> + return write(fd, trigger, strlen(trigger) + 1);
> +}
> +
> +static int pressure_open(const char *resource)
> +{
> + char path[PATH_MAX];
> + int fd;
> +
> + snprintf(path, sizeof(path), "/proc/pressure/%s", resource);
> + fd = open(path, O_RDWR);
> + if (fd < 0)
> + fprintf(stderr, "open %s: %s\n", path, strerror(errno));
Use ksft_perror() instead please.
> + return fd;
> +}
> +
> +FIXTURE(psi)
> +{
> + char root[PATH_MAX];
> + char *cg;
> +};
> +
> +FIXTURE_SETUP(psi)
> +{
> + int psi_fd;
> +
> + self->cg = NULL;
> +
> + if (cg_find_unified_root(self->root, sizeof(self->root), NULL))
> + SKIP(return, "cgroup v2 isn't mounted");
> +
> + /* PSI must be enabled (CONFIG_PSI=y, not disabled on the cmdline). */
> + psi_fd = open("/proc/pressure/memory", O_RDONLY);
> + if (psi_fd < 0)
> + SKIP(return, "PSI unavailable (CONFIG_PSI=n or psi=0)");
> + close(psi_fd);
Why can't cgroup setup be done here? IOW, why not do
self->cg = cg_name(self->root, "psi_trigger_test");
cg_create(self->cg))
here only once? Usually FIXTURE_SETUP and FIXTURE_TEARDOWN are
symmetric: you teardown what you setup.
> +}
> +
> +FIXTURE_TEARDOWN(psi)
> +{
> + if (self->cg) {
> + cg_killall(self->cg);
> + cg_destroy(self->cg);
> + free(self->cg);
> + }
> +}
> +
> +/*
> + * /proc/pressure/<resource> accepts exactly one trigger per file
> + * descriptor. For io, memory and cpu verify that a "some" trigger arms
> + * and that a second trigger on the same fd is rejected with EBUSY.
> + */
> +TEST_F(psi, proc_trigger_io)
> +{
> + int fd;
> +
> + fd = pressure_open("io");
> + ASSERT_GE(fd, 0);
> + ASSERT_GT(write_trigger(fd, "some 150000 2000000"), 0);
> + ASSERT_EQ(-1, write_trigger(fd, "full 150000 2000000"));
> + ASSERT_EQ(EBUSY, errno);
> + close(fd);
> +}
> +
> +TEST_F(psi, proc_trigger_memory)
> +{
> + int fd;
> +
> + fd = pressure_open("memory");
> + ASSERT_GE(fd, 0);
> + ASSERT_GT(write_trigger(fd, "some 150000 2000000"), 0);
> + ASSERT_EQ(-1, write_trigger(fd, "full 150000 2000000"));
> + ASSERT_EQ(EBUSY, errno);
> + close(fd);
> +}
> +
> +TEST_F(psi, proc_trigger_cpu)
> +{
> + int fd;
> +
> + fd = pressure_open("cpu");
> + ASSERT_GE(fd, 0);
> + ASSERT_GT(write_trigger(fd, "some 150000 2000000"), 0);
> + ASSERT_EQ(-1, write_trigger(fd, "full 150000 2000000"));
> + ASSERT_EQ(EBUSY, errno);
> + close(fd);
> +}
proc_trigger_io, proc_trigger_memory and proc_trigger_cpu do almost
the same thing. You can refactor them:
static void test_psi_write(const char *filename)
{
int fd;
fd = pressure_open(filename);
ASSERT_GE(fd, 0);
ASSERT_GT(write_trigger(fd, "some 150000 2000000"), 0);
ASSERT_EQ(-1, write_trigger(fd, "full 150000 2000000"));
ASSERT_EQ(EBUSY, errno);
close(fd);
}
TEST_F(psi, proc_trigger_io)
{
test_psi_write("io");
}
TEST_F(psi, proc_trigger_memory)
{
test_psi_write("memory");
}
TEST_F(psi, proc_trigger_cpu)
{
test_psi_write("cpu");
}
> +
> +/*
> + * irq only tracks "full", so a "some" trigger must be rejected while a
> + * "full" trigger arms. irq is optional -- it only exists with IRQ-time
> + * accounting -- so a missing /proc/pressure/irq is SKIP, not FAIL.
> + */
> +TEST_F(psi, proc_trigger_irq)
> +{
> + int fd;
> +
> + fd = pressure_open("irq");
> + if (fd < 0)
> + SKIP(return, "/proc/pressure/irq unavailable");
> +
> + ASSERT_EQ(-1, write_trigger(fd, "some 150000 2000000"));
> + ASSERT_GT(write_trigger(fd, "full 150000 2000000"), 0);
> + close(fd);
> +}
> +
> +/*
> + * cgroup.pressure gates visibility of the per-resource *.pressure files
> + * inside a cgroup: writing 0 hides them, writing 1 shows them again.
> + * Drive one hide/show cycle and check that memory.pressure appears and
> + * disappears along with it.
> + */
> +TEST_F(psi, cgroup_pressure_toggle)
> +{
> + char buf[BUF_SIZE];
> +
> + self->cg = cg_name(self->root, "psi_toggle_test");
> + ASSERT_NE(NULL, self->cg);
> + ASSERT_EQ(0, cg_create(self->cg));
> +
> + ASSERT_EQ(0, cg_write(self->cg, "cgroup.pressure", "0"));
> + ASSERT_EQ(0, cg_read_strcmp(self->cg, "cgroup.pressure", "0\n"));
> + ASSERT_LT(cg_read(self->cg, "memory.pressure", buf, sizeof(buf)), 0);
> +
> + ASSERT_EQ(0, cg_write(self->cg, "cgroup.pressure", "1"));
> + ASSERT_EQ(0, cg_read_strcmp(self->cg, "cgroup.pressure", "1\n"));
> + ASSERT_GE(cg_read(self->cg, "memory.pressure", buf, sizeof(buf)), 0);
> +}
> +
> +/*
> + * A child that burns CPU forever; stopped by cg_killall() on teardown.
> + * It also dies with the runner, so an interrupted run (e.g. Ctrl-C
> + * during poll()) does not leave orphaned hogs pinning every CPU.
> + */
> +static int hog_cpu(const char *cgroup, void *arg)
> +{
> + prctl(PR_SET_PDEATHSIG, SIGKILL);
> + for (;;) {}
> + return 0;
> +}
> +
> +/*
> + * Arm a "some" trigger on a cgroup's cpu.pressure, oversubscribe the
> + * cgroup with more spinning hogs than there are CPUs, and check that the
> + * trigger fires once the cgroup stalls on CPU.
> + */
> +TEST_F(psi, cgroup_trigger_fire)
> +{
> + char *cpupress;
> + struct pollfd pfd = { .events = POLLPRI };
> + long ncpus;
> + int fd;
> + int i;
> +
> + self->cg = cg_name(self->root, "psi_trigger_test");
> + ASSERT_NE(NULL, self->cg);
> + ASSERT_EQ(0, cg_create(self->cg));
> +
> + cpupress = cg_control(self->cg, "cpu.pressure");
> + ASSERT_NE(NULL, cpupress);
> + fd = open(cpupress, O_RDWR);
> + free(cpupress);
> + ASSERT_GE(fd, 0);
> + pfd.fd = fd;
> +
> + /*
> + * 1usec threshold over a 2s window: any CPU stall fires it. The 2s
> + * window is the smallest unprivileged users are allowed to arm.
> + */
> + ASSERT_GT(write_trigger(fd, "some 1 2000000"), 0);
> +
> + ncpus = sysconf(_SC_NPROCESSORS_ONLN);
> + if (ncpus == -1)
> + TH_LOG("sysconf(_SC_NPROCESSORS_ONLN): %s", strerror(errno));
> + ASSERT_NE(-1, ncpus);
> +
> + /* ncpus+1 hogs guarantee CPU contention inside the cgroup. */
> + for (i = 0; i < ncpus + 1; i++)
> + ASSERT_GE(cg_run_nowait(self->cg, hog_cpu, NULL), 0);
> +
> + ASSERT_EQ(1, poll(&pfd, 1, PSI_POLL_TIMEOUT_MS));
> + ASSERT_NE(0, pfd.revents & POLLPRI);
> + close(fd);
> +}
> +
> +TEST_HARNESS_MAIN
> --
> 2.43.0
>
