linux-kernel - Re: [PATCH] cgroup/cpuset: Disable cpuset_cpumask_can

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Message-ID: <c3354d87-a856-421b-a03e-cda2f1346095@redhat.com>
Date: Mon, 18 Nov 2024 22:28:38 -0500
From: Waiman Long <llong@...hat.com>
To: Juri Lelli <juri.lelli@...hat.com>, Waiman Long <llong@...hat.com>
Cc: Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>,
 Michal Koutný <mkoutny@...e.com>, cgroups@...r.kernel.org,
 linux-kernel@...r.kernel.org, Phil Auld <pauld@...hat.com>
Subject: Re: [PATCH] cgroup/cpuset: Disable cpuset_cpumask_can_shrink() test
 if not load balancing

On 11/18/24 8:58 AM, Waiman Long wrote:
>>> The failing test isn't an isolated partition. The actual test 
>>> failure is
>>>
>>> Test TEST_MATRIX[62] failed result check!
>>> C0-4:X2-4:S+ C1-4:X2-4:S+:P2 C2-4:X4:P1 . . X5 . . 0 
>>> A1:0-4,A2:1-4,A3:2-4
>>> A1:P0,A2:P-2,A3:P-1
>>>
>>> In this particular case, cgroup A3 has the following setting before 
>>> the X5
>>> operation.
>>>
>>> A1/A2/A3/cpuset.cpus: 2-4
>>> A1/A2/A3/cpuset.cpus.exclusive: 4
>>> A1/A2/A3/cpuset.cpus.effective: 4
>>> A1/A2/A3/cpuset.cpus.exclusive.effective: 4
>>> A1/A2/A3/cpuset.cpus.partition: root
>> Right, and is this problematic already?
> We allow nested partition setup. So there can be a child partition 
> underneath a parent partition. So this is OK.
>>
>> Then the test, I believe, does
>>
>> # echo 5 >cgroup/A1/A2/cpuset.cpus.exclusive
>>
>> and that goes through and makes the setup invalid - root domain reconf
>> and the following
>>
>> # cat cgroup/A1/cpuset.cpus.partition
>> member
>> # cat cgroup/A1/A2/cpuset.cpus.partition
>> isolated invalid (Parent is not a partition root)
>> # cat cgroup/A1/A2/A3/cpuset.cpus.partition
>> root invalid (Parent is an invalid partition root)
>>
>> Is this what shouldn't happen?
>>
> A3 should become invalid because none of the CPUs in 
> cpuset.cpus.exclusive can be granted. However A2 should remain a valid 
> partition. I will look further into that. Thank for spotting this 
> inconsistency. 

Sorry, I misread the test. The X5 entry above refers to "echo 5 > 
A1/A2/cpuset.cpus.exclusive" not to A3. This invalidates the A2 
partition which further invalidates the child A3 partition. So the 
result is correct.

Cheers,
Longman