On 05/02/2018 10:08 AM, Peter Zijlstra wrote: > On Thu, Apr 19, 2018 at 09:47:02AM -0400, Waiman Long wrote: >> diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt >> index c970bd7..8d89dc2 100644 >> --- a/Documentation/cgroup-v2.txt >> +++ b/Documentation/cgroup-v2.txt >> @@ -1484,6 +1484,31 @@ Cpuset Interface Files >> a subset of "cpuset.cpus". Its value will be affected by CPU >> hotplug events. >> >> + cpuset.cpus.isolated >> + A read-write multiple values file which exists on root cgroup >> + only. >> + >> + It lists the CPUs that have been withdrawn from the root cgroup >> + for load balancing. These CPUs can still be allocated to child >> + cpusets with load balancing enabled, if necessary. >> + >> + If a child cpuset contains only an exclusive set of CPUs that are >> + a subset of the isolated CPUs and with load balancing enabled, >> + these CPUs will be load balanced on a separate root domain from >> + the one in the root cgroup. >> + >> + Just putting the CPUs into "cpuset.cpus.isolated" will be >> + enough to disable load balancing on those CPUs as long as they >> + do not appear in a child cpuset with load balancing enabled. >> + Fine-grained control of cpu isolation can also be done by >> + putting these isolated CPUs into child cpusets with load >> + balancing disabled. >> + >> + The "cpuset.cpus.isolated" should be set up before child >> + cpusets are created. Once child cpusets are present, changes >> + to "cpuset.cpus.isolated" will not be allowed if the CPUs that >> + change their states are in any of the child cpusets. >> + > So I see why you did this, but it is _really_ ugly and breaks the > container invariant. > > Ideally we'd make the root group less special, not more special.
Yes, I am planning to make the root cgroup less special by putting a new isolation flag into all the non-root cgroup. The container invariant thing, however, is a bit hard to do. Do we really need a container root to behave exactly like the real root? I guess we can make that happen if we really want to, but it will certainly make the code more complex. So it is a trade-off about what is worth to do and what is not. Cheers, Longman
