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Date: Fri, 20 Mar 2020 17:54:57 +0100 From: Vincent Guittot <vincent.guittot@...aro.org> To: Mel Gorman <mgorman@...hsingularity.net> Cc: Ingo Molnar <mingo@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Valentin Schneider <valentin.schneider@....com>, Phil Auld <pauld@...hat.com>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 4/4] sched/fair: Track possibly overloaded domains and abort a scan if necessary On Fri, 20 Mar 2020 at 17:44, Mel Gorman <mgorman@...hsingularity.net> wrote: > > On Fri, Mar 20, 2020 at 04:48:39PM +0100, Vincent Guittot wrote: > > > --- > > > include/linux/sched/topology.h | 1 + > > > kernel/sched/fair.c | 65 +++++++++++++++++++++++++++++++++++++++--- > > > kernel/sched/features.h | 3 ++ > > > 3 files changed, 65 insertions(+), 4 deletions(-) > > > > > > diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h > > > index af9319e4cfb9..76ec7a54f57b 100644 > > > --- a/include/linux/sched/topology.h > > > +++ b/include/linux/sched/topology.h > > > @@ -66,6 +66,7 @@ struct sched_domain_shared { > > > atomic_t ref; > > > atomic_t nr_busy_cpus; > > > int has_idle_cores; > > > + int is_overloaded; > > > > Can't nr_busy_cpus compared to sd->span_weight give you similar status ? > > > > It's connected to nohz balancing and I didn't see how I could use that > for detecting overload. Also, I don't think it ever can be larger than > the sd weight and overload is based on the number of running tasks being > greater than the number of available CPUs. Did I miss something obvious? IIUC you try to estimate if there is a chance to find an idle cpu before starting the loop and scanning the domain and abort early if the possibility is low. if nr_busy_cpus equals to sd->span_weight it means that there is no free cpu so there is no need to scan > > -- > Mel Gorman > SUSE Labs
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