linux-kernel - Re: [PATCH 4/4] sched/fair: Track possibly overloaded domains and abort a scan if necessary

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Date:   Fri, 20 Mar 2020 16:44:32 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Vincent Guittot <vincent.guittot@...aro.org>
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, 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?

-- 
Mel Gorman
SUSE Labs