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

[Joel Fernandes]

On Fri, Oct 23, 2020 at 05:05:44PM +0200, Peter Zijlstra wrote:
> 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?

Yes you are right, we need to delete this bit from the changelog. :-(. I'll
go do that.

thanks,

 - Joel