Re: [PATCH 6/6] sched_ext: Clear the built-in idle masks on CPU hotplug transitions

[Tejun Heo]

Hello, Tao.

On Thu, Nov 12, 2026 at 09:09:34PM +0800, Tao Cui wrote:
> offline CPU as an idle candidate, and the built-in select_cpu path may
> claim it once before the guard layers bounce the wakeup, costing a
> failed pick and a bumped SCX_EV_SELECT_CPU_FALLBACK each time. This is
> not the documented racy and self-correcting regime of the idle SMT
> handling: the stale bit is a deterministic leftover, and read-only
> kfunc consumers never trigger the claim-time self-correction.

The failure mode is benign, and the patch doesn't address even what it
describes. With a scheduler which implements the hotplug ops and only reads
the idle mask, the offline CPU stays set in the mask for the whole offline
window with the patch applied, the same as without it.

Thanks.

--
tejun