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SubjectRe: [PATCH v3 6/9] cgroup/cpuset: Add a new isolated cpus.partition type
On 7/27/21 7:42 AM, Frederic Weisbecker wrote:
> On Tue, Jul 20, 2021 at 10:18:31AM -0400, Waiman Long wrote:
>> Bugzilla:
>> commit 994fb794cb252edd124a46ca0994e37a4726a100
>> Author: Waiman Long <>
>> Date: Sat, 19 Jun 2021 13:28:19 -0400
>> cgroup/cpuset: Add a new isolated cpus.partition type
>> Cpuset v1 uses the sched_load_balance control file to determine if load
>> balancing should be enabled. Cpuset v2 gets rid of sched_load_balance
>> as its use may require disabling load balancing at cgroup root.
>> For workloads that require very low latency like DPDK, the latency
>> jitters caused by periodic load balancing may exceed the desired
>> latency limit.
>> When cpuset v2 is in use, the only way to avoid this latency cost is to
>> use the "isolcpus=" kernel boot option to isolate a set of CPUs. After
>> the kernel boot, however, there is no way to add or remove CPUs from
>> this isolated set. For workloads that are more dynamic in nature, that
>> means users have to provision enough CPUs for the worst case situation
>> resulting in excess idle CPUs.
>> To address this issue for cpuset v2, a new cpuset.cpus.partition type
>> "isolated" is added which allows the creation of a cpuset partition
>> without load balancing. This will allow system administrators to
>> dynamically adjust the size of isolated partition to the current need
>> of the workload without rebooting the system.
>> Signed-off-by: Waiman Long <>
>> Signed-off-by: Waiman Long <>
> Nice! And while we are adding a new ABI, can we take advantage of that and
> add a specific semantic that if a new isolated partition matches a subset of
> "isolcpus=", it automatically maps to it. This means that any further
> modification to that isolated partition will also modify the associated
> isolcpus= subset.
> Or to summarize, when we create a new isolated partition, remove the associated
> CPUs from isolcpus= ?

We can certainly do that as a follow-on. Another idea that I have been
thinking about is to automatically generating a isolated partition under
root to match the given isolcpus parameter when the v2 filesystem is
mounted. That needs more experimentation and testing to verify that it
can work.


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