Re: [PATCH v8 -tip 06/26] sched: Add core wide task selection and scheduling.

[Peter Zijlstra]

On Mon, Oct 19, 2020 at 09:43:16PM -0400, Joel Fernandes (Google) wrote:
> From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> 
> Instead of only selecting a local task, select a task for all SMT
> siblings for every reschedule on the core (irrespective which logical
> CPU does the reschedule).

This:

> 
> During a CPU hotplug event, schedule would be called with the hotplugged
> CPU not in the cpumask. So use for_each_cpu(_wrap)_or to include the
> current cpu in the task pick loop.
> 
> There are multiple loops in pick_next_task that iterate over CPUs in
> smt_mask. During a hotplug event, sibling could be removed from the
> smt_mask while pick_next_task is running. So we cannot trust the mask
> across the different loops. This can confuse the logic. Add a retry logic
> if smt_mask changes between the loops.

isn't entirely accurate anymore, is it?