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

[Joe Simmons-Talbott <josimmon@redhat.com>]

On Thu, Jun 25, 2026 at 04:20:25PM -0400, Joe Simmons-Talbott wrote:
> On Thu, Jun 25, 2026 at 3:54 PM Joe Simmons-Talbott <joest@redhat.com> wrote:
> >
> 
> +mailing lists
> +Tao Cui

I messed this up.  Please ignore this patch.  I will resend.

Thanks,
Joe
> 
> 
> 
> > 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@redhat.com/
> > Signed-off-by: Joe Simmons-Talbott <joest@redhat.com>
> > ---
> > 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
> >