Re: [PATCH] sched_ext: Hold DSQ refs for deferred reenqueues

[Hui Su <sh_def@163.com>]

Hi Tejun,

On Wed, Sep 30, 2026 at 07:15:20AM -1000, Tejun Heo wrote:
> Can you try to do it without refcnts? DSQ destructions are rare events and
> we can reliably detect whether the DSQ is full or not. I'd much rather make
> the destruction path expensive than adding refcnt to hot paths.

Thanks. v3 follows this direction and adds no refcounting to the deferred
reenqueue path. After the initial grace period, the destruction callback
sweeps the per-CPU deferred lists under the rq lock followed by
deferred_reenq_lock, then checks the DSQ list under its lock. If the list is
still non-empty, it retries the callback, which also covers the case where
an active reenq_user() cursor remains; otherwise it proceeds with final
reclamation.

This keeps the additional synchronization on the rare DSQ destruction path.

v3:
https://lore.kernel.org/lkml/20261008024753.4096008-1-sh_def@163.com/

Thanks,
Hui