Re: [RFC PATCH 00/18] cgroup/cpuset: Enable runtime modification of

[Waiman Long <llong@redhat.com>]

On 8/8/25 11:50 AM, Frederic Weisbecker wrote:
> Le Fri, Aug 08, 2025 at 11:10:44AM -0400, Waiman Long a écrit :
>> The "nohz_full" and "rcu_nocbs" boot command parameters can be used to
>> remove a lot of kernel overhead on a specific set of isolated CPUs which
>> can be used to run some latency/bandwidth sensitive workloads with as
>> little kernel disturbance/noise as possible. The problem with this mode
>> of operation is the fact that it is a static configuration which cannot
>> be changed after boot to adjust for changes in application loading.
>>
>> There is always a desire to enable runtime modification of the number
>> of isolated CPUs that can be dedicated to this type of demanding
>> workloads. This patchset is an attempt to do just that with an amount of
>> CPU isolation close to what can be done with the nohz_full and rcu_nocbs
>> boot kernel parameters.
>>
>> This patch series provides the ability to change the set of housekeeping
>> CPUs at run time via the cpuset isolated partition functionality.
>> Currently, the cpuset isolated partition is able to disable scheduler
>> load balancing and the CPU affinity of the unbound workqueue to avoid the
>> isolated CPUs. This patch series will extend that with other kernel noises
>> associated with the nohz_full boot command line parameter which has the
>> following sub-categories:
>>    - tick
>>    - timer
>>    - RCU
>>    - MISC
>>    - WQ
>>    - kthread
> Thanks for working on that, I'm about to leave for 2 weeks vacation so I
> won't have the time to check this until I'm back.
>
> However this series is highly conflicting with mine (cpuset/isolation: Honour
> kthreads preferred affinity). Your patchset even redoes things I'm doing
> (housekeeping cpumask update, RCU synchronization, HK_TYPE_DOMAIN to include
> cpusets, etc...)
>
> I have a v2 that is almost ready to post.
>
> Wouldn't it be better to wait for it and its infrastructure changes before
> proceeding with nohz_full?

Sure. I am just posting this RFC patch series to show my current idea 
that I have. I will wait for your v2 and integrate on top.

Looking forward to your upcoming v2 patch.

Cheers,
Longman