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SubjectRe: [PATCH v8 3/6] cpuset: Add cpuset.sched.load_balance flag to v2
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On 05/24/2018 11:43 AM, Peter Zijlstra wrote:
> On Thu, May 17, 2018 at 04:55:42PM -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 flag is set by the parent and is not delegatable.
>>
>> Signed-off-by: Waiman Long <longman@redhat.com>
>> ---
>> Documentation/cgroup-v2.txt | 24 ++++++++++++++++++++
>> kernel/cgroup/cpuset.c | 53 +++++++++++++++++++++++++++++++++++++++++----
>> 2 files changed, 73 insertions(+), 4 deletions(-)
>>
>> diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
>> index 54d9e22..071b634d 100644
>> --- a/Documentation/cgroup-v2.txt
>> +++ b/Documentation/cgroup-v2.txt
>> @@ -1536,6 +1536,30 @@ Cpuset Interface Files
>> CPUs of the parent cgroup. Once it is set, this flag cannot be
>> cleared if there are any child cgroups with cpuset enabled.
>>
>> + 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.
> I'm confused... why exactly do we have both domain and load_balance ?

The domain is for partitioning the CPUs only. It doesn't change the load
balancing state. So the load_balance flag is still need to turn on and
off load balancing.

Cheers,
Longman

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