Re: [RFC PATCH v4 15/28] sched/rt: Allow zeroing the runtime of the root control group

[Juri Lelli]

Hello,

On 01/12/25 13:41, Yuri Andriaccio wrote:
> In HCBS, the root control group follows the already existing rules for
> rt-task scheduling. As such, it does not make use of the deadline servers
> to account for runtime, or any other HCBS specific code and features.
> 
> While the runtime of SCHED_DEADLINE tasks depends on the global bandwidth
> reserved for rt_tasks, the runtime of SCHED_FIFO/SCHED_RR tasks is limited
> by the activation of fair-servers (as the RT_THROTTLING mechanism has been
> removed in favour of them), thus their maximum bandwidth depends solely on
> the fair-server settings (which are thightly related to the global
> bandwidth reserved for rt-tasks) and the amount of SCHED_OTHER workload to
> run (recall that if no SCHED_OTHER tasks are running, the FIFO/RR tasks
> may fully utilize the CPU).
> 
> The values of runtime and period in the root cgroup's cpu controller do
> not affect, by design of HCBS, the fair-server settings and similar
> (consequently they do not affect the scheduling of FIFO/RR tasks in the
> root cgroup), but they are just used to reserve a portion of the
> SCHED_DEADLINE bandwidth to the scheduling of rt-cgroups. These values
> only affect child cgroups, their deadline servers and their assigned
> FIFO/RR tasks.
> 
> Signed-off-by: Yuri Andriaccio <yurand2000@xxxxxxxxx>

Reviewed-by: Juri Lelli <juri.lelli@xxxxxxxxxx>

Thanks,
Juri