Re: [RFC PATCH 0/5] cgroup/cpuset: A new "isolcpus" paritition
From: Michal Koutný
Date: Tue May 02 2023 - 14:01:25 EST
Hello.
The previous thread arrived incomplete to me, so I respond to the last
message only. Point me to a message URL if it was covered.
On Fri, Apr 14, 2023 at 03:06:27PM -0400, Waiman Long <longman@xxxxxxxxxx> wrote:
> Below is a draft of the new cpuset.cpus.reserve cgroupfs file:
>
> cpuset.cpus.reserve
> A read-write multiple values file which exists on all
> cpuset-enabled cgroups.
>
> It lists the reserved CPUs to be used for the creation of
> child partitions. See the section on "cpuset.cpus.partition"
> below for more information on cpuset partition. These reserved
> CPUs should be a subset of "cpuset.cpus" and will be mutually
> exclusive of "cpuset.cpus.effective" when used since these
> reserved CPUs cannot be used by tasks in the current cgroup.
>
> There are two modes for partition CPUs reservation -
> auto or manual. The system starts up in auto mode where
> "cpuset.cpus.reserve" will be set automatically when valid
> child partitions are created and users don't need to touch the
> file at all. This mode has the limitation that the parent of a
> partition must be a partition root itself. So child partition
> has to be created one-by-one from the cgroup root down.
>
> To enable the creation of a partition down in the hierarchy
> without the intermediate cgroups to be partition roots,
Why would be this needed? Owning a CPU (a resource) must logically be
passed all the way from root to the target cgroup, i.e. this is
expressed by valid partitioning down to given level.
> one
> has to turn on the manual reservation mode by writing directly
> to "cpuset.cpus.reserve" with a value different from its
> current value. By distributing the reserve CPUs down the cgroup
> hierarchy to the parent of the target cgroup, this target cgroup
> can be switched to become a partition root if its "cpuset.cpus"
> is a subset of the set of valid reserve CPUs in its parent.
level n
`- level n+1
cpuset.cpus // these are actually configured by "owner" of level n
cpuset.cpus.partition // similrly here, level n decides if child is a partition
I.e. what would be level n/cpuset.cpus.reserve good for when it can
directly control level n+1/cpuset.cpus?
Thanks,
Michal
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