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    SubjectRe: [PATCH v8 3/6] cpuset: Add cpuset.sched.load_balance flag to v2
    On 24/05/18 11:09, Waiman Long wrote:
    > On 05/24/2018 10:36 AM, Juri Lelli wrote:
    > > On 17/05/18 16:55, Waiman Long wrote:
    > >
    > > [...]
    > >
    > >> + A parent cgroup cannot distribute all its CPUs to child
    > >> + scheduling domain cgroups unless its load balancing flag is
    > >> + turned off.
    > >> +
    > >> + cpuset.sched.load_balance
    > >> + 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 a non-zero value (on). This flag is set
    > >> + by the parent and is not delegatable.
    > >> +
    > >> + When it is on, tasks within this cpuset will be load-balanced
    > >> + by the kernel scheduler. Tasks will be moved from CPUs with
    > >> + high load to other CPUs within the same cpuset with less load
    > >> + periodically.
    > >> +
    > >> + When it is off, there will be no load balancing among CPUs on
    > >> + this cgroup. Tasks will stay in the CPUs they are running on
    > >> + and will not be moved to other CPUs.
    > >> +
    > >> + The initial value of this flag is "1". This flag is then
    > >> + inherited by child cgroups with cpuset enabled. Its state
    > >> + can only be changed on a scheduling domain cgroup with no
    > >> + cpuset-enabled children.
    > > [...]
    > >
    > >> + /*
    > >> + * On default hierachy, a load balance flag change is only allowed
    > >> + * in a scheduling domain with no child cpuset.
    > >> + */
    > >> + if (cgroup_subsys_on_dfl(cpuset_cgrp_subsys) && balance_flag_changed &&
    > >> + (!is_sched_domain(cs) || css_has_online_children(&cs->css))) {
    > >> + err = -EINVAL;
    > >> + goto out;
    > >> + }
    > > The rule is actually
    > >
    > > - no child cpuset
    > > - and it must be a scheduling domain
    > >
    > > Right?
    >
    > Yes, because it doesn't make sense to have a cpu in one cpuset that has
    > loading balance off while, at the same time, in another cpuset with load
    > balancing turned on. This restriction is there to make sure that the
    > above condition will not happen. I may be wrong if there is a realistic
    > use case where the above condition is desired.

    Yep, makes sense to me.

    Maybe add the second condition to the comment and documentation.

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