On Thu, May 17, 2018 at 04:55:41PM -0400, Waiman Long wrote: > A new cpuset.sched.domain boolean flag is added to cpuset v2. This new > flag indicates that the CPUs in the current cpuset should be treated > as a separate scheduling domain.
The traditional name for this is a partition. > This new flag is owned by the parent > and will cause the CPUs in the cpuset to be removed from the effective > CPUs of its parent. This is a significant departure from existing behaviour, but one I can appreciate. I don't immediately see something terribly wrong with it. > This is implemented internally by adding a new isolated_cpus mask that > holds the CPUs belonging to child scheduling domain cpusets so that: > > isolated_cpus | effective_cpus = cpus_allowed > isolated_cpus & effective_cpus = 0 > > This new flag can only be turned on in a cpuset if its parent is either > root or a scheduling domain itself with non-empty cpu list. The state > of this flag cannot be changed if the cpuset has children. > > Signed-off-by: Waiman Long <long...@redhat.com> > --- > Documentation/cgroup-v2.txt | 22 ++++ > kernel/cgroup/cpuset.c | 237 > +++++++++++++++++++++++++++++++++++++++++++- > 2 files changed, 256 insertions(+), 3 deletions(-) > > diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt > index cf7bac6..54d9e22 100644 > --- a/Documentation/cgroup-v2.txt > +++ b/Documentation/cgroup-v2.txt > @@ -1514,6 +1514,28 @@ Cpuset Interface Files > it is a subset of "cpuset.mems". Its value will be affected > by memory nodes hotplug events. > > + cpuset.sched.domain > + 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). I would be conservative and only allow 0/1. > This flag is set > + by the parent and is not delegatable. > + > + If set, it indicates that the CPUs in the current cgroup will > + be the root of a scheduling domain. The root cgroup is always > + a scheduling domain. 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 parent cgroup is also a scheduling domain with a non-empty > + cpu list. Ah, so initially I was confused by the requirement for root to have it always set, but you'll allow child domains to steal _all_ CPUs, such that root ends up with an empty effective set? What about the (kernel) threads that cannot be moved out of the root group? > + 2) The list of CPUs are exclusive, i.e. they are not shared by > + any of its siblings. Right. > + 3) There is no child cgroups with cpuset enabled. > + > + 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. This I'm not clear on. Why?
