[PATCH 06/10] sched/fair: Clear the target CPU from the cpumask of CPUs searched

[Mel Gorman]

On Fri, Dec 04, 2020 at 02:47:48PM +0100, Vincent Guittot wrote:
> > IIUC, select_idle_core and select_idle_cpu share the same cpumask(select_idle_mask)?
> > If the target's sibling is removed from select_idle_mask from select_idle_core(),
> > select_idle_cpu() will lose the chance to pick it up?
> 
> This is only relevant for patch 10 which is not to be included IIUC
> what mel said in cover letter : "Patches 9 and 10 are stupid in the
> context of this series."
> 

Patch 10 was stupid in the context of the prototype because
select_idle_core always returned a CPU. A variation ended up being
reintroduced at the end of the Series Yet To Be Posted so that SMT siblings
are cleared during select_idle_core() but select_idle_cpu() still has a
mask with unvisited CPUs to consider if no idle cores are found.

As far as I know, this would still be compatible with Aubrey's idle
cpu mask as long as it's visited and cleared between select_idle_core
and select_idle_cpu. It relaxes the contraints on Aubrey to some extent
because the idle cpu mask would be a hint so if the information is out
of date, an idle cpu may still be found the normal way.

-- 
Mel Gorman
SUSE Labs