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

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Message-ID: <ZzwqFkzGACnbiTJW@jlelli-thinkpadt14gen4.remote.csb>
Date: Tue, 19 Nov 2024 07:03:02 +0100
From: Juri Lelli <juri.lelli@...hat.com>
To: 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 18/11/24 22:28, Waiman Long wrote:
> 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.

OK, makes sense to me. But so, the test doesn't actually fail? Sorry,
guess I'm confused. :)