Messages in this thread | | | From | Vincent Guittot <> | Date | Fri, 4 Dec 2020 14:47:48 +0100 | Subject | Re: [PATCH 06/10] sched/fair: Clear the target CPU from the cpumask of CPUs searched |
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On Fri, 4 Dec 2020 at 14:40, Li, Aubrey <aubrey.li@linux.intel.com> wrote: > > On 2020/12/4 21:17, Vincent Guittot wrote: > > On Fri, 4 Dec 2020 at 14:13, Vincent Guittot <vincent.guittot@linaro.org> wrote: > >> > >> On Fri, 4 Dec 2020 at 12:30, Mel Gorman <mgorman@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."
> > Thanks, > -Aubrey
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