On Fri, Dec 04, 2020 at 11:56:36AM +0100, Vincent Guittot wrote: > > The intent was that the sibling might still be an idle candidate. In > > the current draft of the series, I do not even clear this so that the > > SMT sibling is considered as an idle candidate. The reasoning is that if > > there are no idle cores then an SMT sibling of the target is as good an > > idle CPU to select as any. > > Isn't the purpose of select_idle_smt ? >
Only in part. > select_idle_core() looks for an idle core and opportunistically saves > an idle CPU candidate to skip select_idle_cpu. In this case this is > useless loops for select_idle_core() because we are sure that the core > is not idle > If select_idle_core() finds an idle candidate other than the sibling, it'll use it if there is no idle core -- it picks a busy sibling based on a linear walk of the cpumask. Similarly, select_idle_cpu() is not guaranteed to scan the sibling first (ordering) or even reach the sibling (throttling). select_idle_smt() is a last-ditch effort. -- Mel Gorman SUSE Labs
