Re: [RFC PATCH 0/1] sched/fair: Feature to suppress Fair Server for NOHZ_FULL isolation

[Valentin Schneider]

On 06/01/26 14:37, Shrikanth Hegde wrote:
> On 1/6/26 9:12 AM, Aaron Tomlin wrote:
>> Hi Ingo, Peter, Juri, Vincent,
>>
>> This patch introduces a new scheduler feature, RT_SUPPRESS_FAIR_SERVER,
>> designed to ensure strict NOHZ_FULL isolation for SCHED_FIFO workloads,
>> particularly in the presence of resident CFS tasks.
>>
>> In strictly partitioned, latency-critical environments (such as High
>> Frequency Trading platforms) administrators frequently employ fully
>> adaptive-tick CPUs to execute pinned SCHED_FIFO workloads. The fundamental
>> requirement is "zero OS noise"; specifically, the scheduler clock-tick must
>> remain suppressed ("offloaded"), given that standard SCHED_FIFO semantics
>> dictate no forced preemption between tasks of identical priority.
>
> If all your SCHED_FIFO is pinned and their scheduling decisions
> are managed in userspace, using isolcpus would offer you better
> isolations compared to nohz_full.
>

Right, that's the part I don't get; why not use CPU isolation / cpusets to
isolate the CPUs running those NOHZ_FULL applications? Regardless of the
deadline server, if CFS tasks get scheduled on the same CPU as your
latency-sensitive tasks then something's not right.