[linus:master] [selftests/cgroup] 954bacce36: kernel-selftests.cgroup.test_cpu.test_cpucg_max.fail

[linus:master] [selftests/cgroup] 954bacce36: kernel-selftests.cgroup.test_cpu.test_cpucg_max.fail

[kernel test robot]

Hello,


we noticed 954bacce36 is to address "cpu.max tests", however, we found below
two tests can pass on parent, but failed on 954bacce36.

dfe25fbaedfc2a07 954bacce36d976fe472090b5598
---------------- ---------------------------
       fail:runs  %reproduction    fail:runs
           |             |             |
           :6           100%          6:6     kernel-selftests.cgroup.test_cpu.test_cpucg_max.fail
           :6           100%          6:6     kernel-selftests.cgroup.test_cpu.test_cpucg_max_nested.fail


not sure if there are any necessary env setting? thanks


kernel test robot noticed "kernel-selftests.cgroup.test_cpu.test_cpucg_max.fail" on:

commit: 954bacce36d976fe472090b55987df66da00c49b ("selftests/cgroup: fix cpu.max tests")
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master

[test failed on linux-next/master 84b92a499e7eca54ba1df6f6c6e01766025943f1]

in testcase: kernel-selftests
version: kernel-selftests-x86_64-ae388edd4a8f-1_20250729
with following parameters:

	group: cgroup



config: x86_64-rhel-9.4-kselftests
compiler: gcc-12
test machine: 4 threads 1 sockets Intel(R) Core(TM) i3-3220 CPU @ 3.30GHz (Ivy Bridge) with 8G memory

(please refer to attached dmesg/kmsg for entire log/backtrace)


If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <oliver.sang@intel.com>
| Closes: https://lore.kernel.org/oe-lkp/202508070722.46239e7c-lkp@intel.com



# timeout set to 300
# selftests: cgroup: test_cpu
# ok 1 test_cpucg_subtree_control
# ok 2 test_cpucg_stats
# ok 3 test_cpucg_nice
# not ok 4 test_cpucg_weight_overprovisioned
# ok 5 test_cpucg_weight_underprovisioned
# not ok 6 test_cpucg_nested_weight_overprovisioned
# ok 7 test_cpucg_nested_weight_underprovisioned
# not ok 8 test_cpucg_max
# not ok 9 test_cpucg_max_nested
not ok 2 selftests: cgroup: test_cpu # exit=1



The kernel config and materials to reproduce are available at:
https://download.01.org/0day-ci/archive/20250807/202508070722.46239e7c-lkp@intel.com



-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [linus:master] [selftests/cgroup] 954bacce36: kernel-selftests.cgroup.test_cpu.test_cpucg_max.fail

[Michal Koutný]

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Hello.

On Thu, Aug 07, 2025 at 01:52:31PM +0800, kernel test robot <oliver.sang@intel.com> wrote:
> dfe25fbaedfc2a07 954bacce36d976fe472090b5598
> ---------------- ---------------------------
>        fail:runs  %reproduction    fail:runs
>            |             |             |
>            :6           100%          6:6     kernel-selftests.cgroup.test_cpu.test_cpucg_max.fail
>            :6           100%          6:6     kernel-selftests.cgroup.test_cpu.test_cpucg_max_nested.fail
> 
> 
> not sure if there are any necessary env setting? thanks

The selftest commit essentially changed the tolerance margin from
ridiculously large to something that looked statistically appropriate
[1].
However, when I run the test (30x) on the 954bacce36 I get:

quantile([D1 D2 D8])  # 1 2 and 8 vCPUs respectively
ans =

   1.3086e+04   1.1559e+04   1.1177e+04 # min
   1.5109e+04   1.2936e+04   1.2989e+04
   1.5791e+04   1.3938e+04   1.3788e+04 # median
   1.6159e+04   1.5385e+04   1.4980e+04
   1.8757e+04   1.8699e+04   1.9494e+04 # max

I obtain similar values also on v6.15 (the kernel + 954bacce36
selftest). So it's not anything in throtlling implementation affecting
this.

The tests above were with HZ=250, for HZ=1000, I get slightly smaller
results with D2:
   1.1753e+04 # min
   1.2634e+04
   1.3208e+04 # median
   1.4010e+04
   1.6937e+04 # max

But still nowhere the 20% margin (i.e. values_close(...10%)), these
values would demand up to 100% (values_close(..., 50%)). Or add a bias
derived from sched_cfs_bandwidth_slice_us or increase the tested quota
from 1% to 5%, that'd be an improvement:

   48882 # min
   52450
   52941 # median
   54284 # 75th percentile
   73186 # max (limit would be 60000)

I'm not sure how big overrun we want to accept as a pass.

Michal

[1] lore.kernel.org/r/20250701-kselftest-cgroup-fix-cpu-max-v1-2-049507ad6832@sony.com

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