Re: [PATCH v4 16/26] sched/deadline: Record the root domain holding a task's bandwidth

[Mathieu Desnoyers]

On 2026-11-06 21:35, sashiko-bot@xxxxxxxxxx wrote:
> dl_task_undepart() loses departed state on PI boost

This is the case that the v4 cover lists under "Not changed". A boosted
departed task counts as a deadline task. A rebuild meanwhile counts it
once, where it runs, and records that CPU. The deboost then releases it
from there. A deboost that races the rebuild drops the bandwidth until
its 0-lag time. dl_bw_gen then keeps the release from removing anything.

The move in (ii) is admitted in the destination by cpuset_can_attach(),
as for any deadline task. In (iii) the walk counts each deadline task
from zero, and the release removes it once. v5 documents the deboost
race in the comments.

> stale dl_bw_cpu when dl_bw is zero misroutes bandwidth

Right. No move updates the record of a bandwidth of 0. v5 makes
sched_dl_overflow() use the task's CPU for it, and adds a selftest case.

Thanks,

Mathieu

--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com