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From: Waiman Long <>
To: Tejun Heo <>, Waiman Long <>
Cc: "Zefan Li" <>,
	"Johannes Weiner" <>,
	"Jonathan Corbet" <>,
	"Shuah Khan" <>,,,,,
	"Andrew Morton" <>,
	"Roman Gushchin" <>, "Phil Auld" <>,
	"Peter Zijlstra" <>,
	"Juri Lelli" <>,
	"Frederic Weisbecker" <>,
	"Marcelo Tosatti" <>,
	"Michal Koutný" <>
Subject: Re: [PATCH v7 5/6] cgroup/cpuset: Update description of cpuset.cpus.partition in cgroup-v2.rst
Date: Fri, 27 Aug 2021 21:14:01 -0400	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On 8/27/21 7:35 PM, Tejun Heo wrote:
> Hello,
> On Fri, Aug 27, 2021 at 06:50:10PM -0400, Waiman Long wrote:
>> The cpu exclusivity rule is due to the setting of CPU_EXCLUSIVE bit. This is
>> a pre-existing condition unless you want to change how the
>> cpuset.cpu_exclusive works.
>> So the new rules will be:
>> 1) The "cpuset.cpus" is not empty and the list of CPUs are exclusive.
> Empty cpu list can be considered an exclusive one.
It doesn't make sense to me to have a partition with no cpu configured 
at all. I very much prefer the users to set cpuset.cpus first before 
turning it into a partition.
>> 2) The parent cgroup is a partition root (can be an invalid one).
> Does this mean a partition parent can't stop being a partition if one or
> more of its children become partitions? If so, it violates the rule that a
> descendant shouldn't be able to restrict what its ancestors can do.

No. As I said in the documentation, transitioning from partition root to 
member is allowed. Against, it is illogical to allow a cpuset to become 
a potential partition if it parent is not even a partition root at all. 
In the case that the parent is reverted back to a member, the child 
partitions will stay invalid forever unless the parent become a valid 
partition again.

>> 3) The "cpuset.cpus" is a subset of the parent's cpuset.cpus.allowed.
> Why not just go by effective? This would mean that a parent can't withdraw
> CPUs from its allowed set once descendants are configured. Restrictions like
> this are fine when the entire hierarchy is configured by a single entity but
> become awkward when configurations are multi-tiered, automated and dynamic.

The original rule is to be based on effective cpus. However, to properly 
handle the case of allowing offlined cpus to be included in the 
partition, I have to change it to cpu_allowed instead. I can certainly 
change it back to effective if you prefer.

>> 4) No child cgroup with cpuset enabled.
> idk, maybe? I'm having a hard time seeing the point in adding these
> restrictions when the state transitions are asynchronous anyway. Would it
> help if we try to separate what's absoluately and technically necessary and
> what seems reasonable or high bar and try to justify why each of the latter
> should be added?

This rule is there mainly for ease of implementation. Otherwise, I need 
to add additional code to handle the conversion of child cpusets which 
can be rather complex and require a lot more debugging. This rule will 
no longer apply once the cpuset becomes a partition root.


  reply	other threads:[~2021-08-28  1:14 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-25 21:37 [PATCH v7 0/6] cgroup/cpuset: Add new cpuset partition type & empty effecitve cpus Waiman Long
2021-08-25 21:37 ` [PATCH v7 1/6] cgroup/cpuset: Properly transition to invalid partition Waiman Long
2021-08-25 21:37 ` [PATCH v7 2/6] cgroup/cpuset: Show invalid partition reason string Waiman Long
2021-08-25 21:37 ` [PATCH v7 3/6] cgroup/cpuset: Add a new isolated cpus.partition type Waiman Long
2021-08-25 21:37 ` [PATCH v7 4/6] cgroup/cpuset: Allow non-top parent partition to distribute out all CPUs Waiman Long
2021-08-25 21:37 ` [PATCH v7 5/6] cgroup/cpuset: Update description of cpuset.cpus.partition in cgroup-v2.rst Waiman Long
2021-08-26 17:35   ` Tejun Heo
2021-08-27  3:01     ` Waiman Long
2021-08-27  4:00       ` Tejun Heo
2021-08-27 21:19         ` Waiman Long
2021-08-27 21:27           ` Tejun Heo
2021-08-27 22:50             ` Waiman Long
2021-08-27 23:35               ` Tejun Heo
2021-08-28  1:14                 ` Waiman Long [this message]
     [not found]                 ` <>
2021-10-12 14:39                   ` Michal Koutný
2021-10-13 21:45                     ` Waiman Long
2021-10-13 22:11                       ` Waiman Long
2021-08-30 17:59               ` Michal Koutný
2021-08-25 21:37 ` [PATCH v7 6/6] kselftest/cgroup: Add cpuset v2 partition root state test Waiman Long

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