Re: [PATCH v4] selftests/cgroup: Adjust cpu test duration based on HZ

[Joe Simmons-Talbott]

On Thu, Jun 25, 2026 at 3:54 PM Joe Simmons-Talbott <joest@xxxxxxxxxx> wrote:
>

+mailing lists
+Tao Cui



> For lower HZ values a quota of 1000us is much lower than the amount
> of microseconds per tick which makes the tests test_cpucg_max and
> test_cpugc_max_nested fail. Increase the test duration to accommodate
> for lower HZ values.
>
> Link: https://lore.kernel.org/lkml/20260624160358.430354-1-joest@xxxxxxxxxx/
> Signed-off-by: Joe Simmons-Talbott <joest@xxxxxxxxxx>
> ---
> v3 -> v4:
> - Use usec for adjusting test duration for better accuracy.
> - Remove underscore from static function
> - Use 1000 as the fallback value for hz since it's the default.
>
> v2 -> v3:
> - Instead of changing cpu.max quota extend the test duration based on
>   the HZ value.
> - don't call pclose() if popen() fails.
> - check return value of fscanf().
>
> v1 -> v2:
> - Try checking /proc/config.gz to get the actual kernel HZ value and
>   fallback to 1000 if the value cannot be determined.
>
>  .../cgroup/lib/include/cgroup_util.h          |  1 +
>  tools/testing/selftests/cgroup/test_cpu.c     | 47 ++++++++++++++++---
>  2 files changed, 42 insertions(+), 6 deletions(-)
>
> diff --git a/tools/testing/selftests/cgroup/lib/include/cgroup_util.h b/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
> index febc1723d090..8ebb2b4d4ec0 100644
> --- a/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
> +++ b/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
> @@ -8,6 +8,7 @@
>
>  #define MB(x) (x << 20)
>
> +#define NSEC_PER_USEC  1000L
>  #define USEC_PER_SEC   1000000L
>  #define NSEC_PER_SEC   1000000000L
>
> diff --git a/tools/testing/selftests/cgroup/test_cpu.c b/tools/testing/selftests/cgroup/test_cpu.c
> index 7a40d76b9548..1f280c1db68a 100644
> --- a/tools/testing/selftests/cgroup/test_cpu.c
> +++ b/tools/testing/selftests/cgroup/test_cpu.c
> @@ -639,6 +639,31 @@ test_cpucg_nested_weight_underprovisioned(const char *root)
>         return run_cpucg_nested_weight_test(root, false);
>  }
>
> +/*
> + * Best effort attempt to get the kernel's HZ value from the config.
> + * Return the HZ value if found otherwise return 1000 (the default) to
> + * indicate failure.
> + */
> +static long
> +get_config_hz(void)
> +{
> +       long hz = 1000;
> +       FILE *f;
> +       char cmd[256] = "zcat /proc/config.gz 2>/dev/null | grep '^CONFIG_HZ='";
> +
> +       f = popen(cmd, "r");
> +
> +       if (!f)
> +               return hz;
> +
> +       if (fscanf(f, "CONFIG_HZ=%ld", &hz) == EOF)
> +               goto out;
> +
> +out:
> +       pclose(f);
> +       return hz;
> +}
> +
>  /*
>   * This test creates a cgroup with some maximum value within a period, and
>   * verifies that a process in the cgroup is not overscheduled.
> @@ -646,15 +671,20 @@ test_cpucg_nested_weight_underprovisioned(const char *root)
>  static int test_cpucg_max(const char *root)
>  {
>         int ret = KSFT_FAIL;
> +       long hz = get_config_hz();
>         long quota_usec = 1000;
>         long default_period_usec = 100000; /* cpu.max's default period */
>         long duration_seconds = 1;
>
> -       long duration_usec = duration_seconds * USEC_PER_SEC;
> +       long duration_usec, duration_sec, duration_nsec;
>         long usage_usec, n_periods, remainder_usec, expected_usage_usec;
>         char *cpucg;
>         char quota_buf[32];
>
> +       duration_usec = duration_seconds * USEC_PER_SEC * 1000 / hz;
> +       duration_sec = duration_usec / USEC_PER_SEC;
> +       duration_nsec = duration_usec % USEC_PER_SEC * NSEC_PER_USEC;
> +
>         snprintf(quota_buf, sizeof(quota_buf), "%ld", quota_usec);
>
>         cpucg = cg_name(root, "cpucg_test");
> @@ -670,8 +700,8 @@ static int test_cpucg_max(const char *root)
>         struct cpu_hog_func_param param = {
>                 .nprocs = 1,
>                 .ts = {
> -                       .tv_sec = duration_seconds,
> -                       .tv_nsec = 0,
> +                       .tv_sec = duration_sec,
> +                       .tv_nsec = duration_nsec,
>                 },
>                 .clock_type = CPU_HOG_CLOCK_WALL,
>         };
> @@ -710,15 +740,20 @@ static int test_cpucg_max(const char *root)
>  static int test_cpucg_max_nested(const char *root)
>  {
>         int ret = KSFT_FAIL;
> +       long hz = get_config_hz();
>         long quota_usec = 1000;
>         long default_period_usec = 100000; /* cpu.max's default period */
>         long duration_seconds = 1;
>
> -       long duration_usec = duration_seconds * USEC_PER_SEC;
> +       long duration_usec, duration_sec, duration_nsec;
>         long usage_usec, n_periods, remainder_usec, expected_usage_usec;
>         char *parent, *child;
>         char quota_buf[32];
>
> +       duration_usec = duration_seconds * USEC_PER_SEC * 1000 / hz;
> +       duration_sec = duration_usec / USEC_PER_SEC;
> +       duration_nsec = duration_usec % USEC_PER_SEC * NSEC_PER_USEC;
> +
>         snprintf(quota_buf, sizeof(quota_buf), "%ld", quota_usec);
>
>         parent = cg_name(root, "cpucg_parent");
> @@ -741,8 +776,8 @@ static int test_cpucg_max_nested(const char *root)
>         struct cpu_hog_func_param param = {
>                 .nprocs = 1,
>                 .ts = {
> -                       .tv_sec = duration_seconds,
> -                       .tv_nsec = 0,
> +                       .tv_sec = duration_sec,
> +                       .tv_nsec = duration_nsec,
>                 },
>                 .clock_type = CPU_HOG_CLOCK_WALL,
>         };
> --
> 2.54.0
>