Re: [PATCH v10 2/9] cpuset: Add new v2 cpuset.sched.domain_root flag

Peter Zijlstra
2018-06-20T14:28:02Z

On Mon, Jun 18, 2018 at 12:14:01PM +0800, Waiman Long wrote:
> + cpuset.sched.domain_root

Why are we calling this a domain_root and not a partition?

> + A read-write single value file which exists on non-root
> + cpuset-enabled cgroups. It is a binary value flag that accepts
> + either "0" (off) or "1" (on). This flag is set by the parent
> + and is not delegatable.

You still haven't answered:

https://lkml.kernel.org/r/20180531094943.GG12180@hirez.programming.kicks-ass.net

the question stands.

> + If set, it indicates that the current cgroup is the root of a
> + new scheduling domain or partition that comprises itself and
> + all its descendants except those that are scheduling domain
> + roots themselves and their descendants. The root cgroup is
> + always a scheduling domain root.
> +
> + There are constraints on where this flag can be set. It can
> + only be set in a cgroup if all the following conditions are true.
> +
> + 1) The "cpuset.cpus" is not empty and the list of CPUs are
> + exclusive, i.e. they are not shared by any of its siblings.
> + 2) The "cpuset.cpus" is also a proper subset of the parent's
> + "cpuset.cpus.effective".
> + 3) The parent cgroup is a scheduling domain root.
> + 4) There is no child cgroups with cpuset enabled. This is
> + for eliminating corner cases that have to be handled if such
> + a condition is allowed.
> +
> + Setting this flag will take the CPUs away from the effective
> + CPUs of the parent cgroup. Once it is set, this flag cannot be
> + cleared if there are any child cgroups with cpuset enabled.
> +
> + A parent scheduling domain root cgroup cannot distribute
> + all its CPUs to its child scheduling domain root cgroups.
> + There must be at least one cpu left in the parent scheduling
> + domain root cgroup.