linux-kernel - [PATCH 0/2] selftests/cgroup: better bound for cpu.max tests

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Message-Id: <20250701-kselftest-cgroup-fix-cpu-max-v1-0-049507ad6832@sony.com>
Date: Tue, 01 Jul 2025 23:13:54 +0900
From: Shashank Balaji <shashank.mahadasyam@...y.com>
To: Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>, 
 Michal Koutný <mkoutny@...e.com>, 
 Shuah Khan <shuah@...nel.org>
Cc: cgroups@...r.kernel.org, linux-kselftest@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Shinya Takumi <shinya.takumi@...y.com>, 
 Shashank Balaji <shashank.mahadasyam@...y.com>
Subject: [PATCH 0/2] selftests/cgroup: better bound for cpu.max tests

cpu.max selftests (both the normal one and the nested one) test the
working of throttling by setting up cpu.max, running a cpu hog process
for a specified duration, and comparing usage_usec as reported by
cpu.stat with the duration of the cpu hog: they should be far enough.

Currently, this is done by using values_close, which has two problems:

1. Semantic: values_close is used with an error percentage of 95%, which
   one will not expect on seeing "values close". The intent it's
actually going for is "values far".

2. Accuracy: the tests can pass even if usage_usec is upto around double
   the expected amount. That's too high of a margin for usage_usec.

Overall, this patchset improves the readability and accuracy of the
cpu.max tests.

Signed-off-by: Shashank Balaji <shashank.mahadasyam@...y.com>
---
Shashank Balaji (2):
      selftests/cgroup: rename `expected` to `duration` in cpu.max tests
      selftests/cgroup: better bound in cpu.max tests

 tools/testing/selftests/cgroup/test_cpu.c | 42 ++++++++++++++++++-------------
 1 file changed, 24 insertions(+), 18 deletions(-)
---
base-commit: 66701750d5565c574af42bef0b789ce0203e3071
change-id: 20250227-kselftest-cgroup-fix-cpu-max-56619928e99b

Best regards,
-- 
Shashank Balaji <shashank.mahadasyam@...y.com>