On 2020/12/4 21:47, Vincent Guittot wrote: > On Fri, 4 Dec 2020 at 14:40, Li, Aubrey <aubrey...@linux.intel.com> wrote: >> >> 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? > > 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."
So the target's sibling can be removed from cpumask in select_idle_core in patch 6, and need to be added back in select_idle_core in patch 10, :)
