Re: [RFC PATCH 0/8] cgroup/cpuset: Support RCU_NOCB on isolated partitions

Waiman Long
2024-02-11T01:46:49Z

On 1/19/24 05:24, Paul E. McKenney wrote:
> On Wed, Jan 17, 2024 at 11:35:03AM -0500, Waiman Long wrote:
>> This patch series is based on the RFC patch from Frederic [1]. Instead
>> of offering RCU_NOCB as a separate option, it is now lumped into a
>> root-only cpuset.cpus.isolation_full flag that will enable all the
>> additional CPU isolation capabilities available for isolated partitions
>> if set. RCU_NOCB is just the first one to this party. Additional dynamic
>> CPU isolation capabilities will be added in the future.
>>
>> The first 2 patches are adopted from Federic with minor twists to fix
>> merge conflicts and compilation issue. The rests are for implementing
>> the new cpuset.cpus.isolation_full interface which is essentially a flag
>> to globally enable or disable full CPU isolation on isolated partitions.
>> On read, it also shows the CPU isolation capabilities that are currently
>> enabled. RCU_NOCB requires that the rcu_nocbs option be present in
>> the kernel boot command line. Without that, the rcu_nocb functionality
>> cannot be enabled even if the isolation_full flag is set. So we allow
>> users to check the isolation_full file to verify that if the desired
>> CPU isolation capability is enabled or not.
>>
>> Only sanity checking has been done so far. More testing, especially on
>> the RCU side, will be needed.
> There has been some discussion of simplifying the (de-)offloading code
> to handle only offline CPUs. Along with some discussion of eliminating
> the (de-)offloading capability altogehter.
>
> We clearly should converge on the capability to be provided before
> exposing this to userspace. ;-)

Would you mind giving me a pointer to the discussion of simplifying the
de-offloading code to  handle only offline CPUs?

Thanks,
Longman