On 2020/12/4 21:17, Vincent Guittot wrote: > On Fri, 4 Dec 2020 at 14:13, Vincent Guittot <vincent.guit...@linaro.org> > wrote: >> >> On Fri, 4 Dec 2020 at 12:30, Mel Gorman <mgor...@techsingularity.net> wrote: >>> >>> 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 >> >> My point is that it's a waste of time to loop the sibling cpus of >> target in select_idle_core because it will not help to find an idle >> core. The sibling cpus will then be check either by select_idle_cpu >> of select_idle_smt > > also, while looping the cpumask, the sibling cpus of not idle cpu are > removed and will not be check >
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? Thanks, -Aubrey
