On Tue, May 29, 2018 at 09:41:30AM -0400, Waiman Long wrote: > The sched.load_balance flag is needed to enable CPU isolation similar to > what can be done with the "isolcpus" kernel boot parameter. Its value > can only be changed in a scheduling domain with no child cpusets. On > a non-scheduling domain cpuset, the value of sched.load_balance is > inherited from its parent. This is to make sure that all the cpusets > within the same scheduling domain or partition has the same load > balancing state. > > This flag is set by the parent and is not delegatable. > + cpuset.sched.domain_root > + 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. > + > + 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 parent cgroup is also a scheduling domain root. > + 3) 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. > + Further changes made to "cpuset.cpus" is allowed as long as > + the first condition above is still true. > + > + A parent scheduling domain root cgroup cannot distribute all > + its CPUs to its child scheduling domain root 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 "1" (on). This flag is set by the parent > + and is not delegatable. It is on by default in the root cgroup. > + > + 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 load balancing state of a cgroup can only be changed on a > + scheduling domain root cgroup with no cpuset-enabled children. > + All cgroups within a scheduling domain or partition must have > + the same load balancing state. As descendant cgroups of a > + scheduling domain root are created, they inherit the same load > + balancing state of their root. I still find all that a bit weird. So load_balance=0 basically changes a partition into a 'fully-partitioned partition' with the seemingly random side-effect that now sub-partitions are allowed to consume all CPUs. The rationale, only given in the Changelog above, seems to be to allow 'easy' emulation of isolcpus. I'm still not convinced this is a useful knob to have. You can do fully-partitioned by simply creating a lot of 1 cpu parititions. So this one knob does two separate things, both of which seem, to me, redundant. Can we please get better rationale for this? -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
