On 05/24/2018 11:41 AM, Peter Zijlstra wrote: > 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. Do you want to call it cpuset.sched.partition? That name sounds strange to me. >> 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 <longman@xxxxxxxxxx> >> --- >> 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. I stated that because echoing other integer value like 2 into the flag file won't return any error. I will modify it to say just 0 and 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? Actually, the current code won't allow you to take all the CPUs from a scheduling domain cpuset with load balancing on. So there must be at least 1 cpu left. You can take all away if load balancing is off. >> + 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? > That is for pragmatic reason as it is easier to code this way. We could remove this restriction but that will make the code more complex. Cheers, Longman -- 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
