On 05/24/2018 11:16 AM, Juri Lelli wrote:
> 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.
Sure. Will do.
-Longman
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