linux-kernel - Re: [PATCH 4/4] sched/numa: Do not move imbalanced load purely on the basis of an idle CPU

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Message-ID: <20180907123739.GE1719@techsingularity.net>
Date:   Fri, 7 Sep 2018 13:37:39 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] sched/numa: Do not move imbalanced load purely on
 the basis of an idle CPU

On Fri, Sep 07, 2018 at 01:33:09PM +0200, Peter Zijlstra wrote:
> > ---
> >  kernel/sched/fair.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index d59d3e00a480..d4c289c11012 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -1560,7 +1560,7 @@ static bool task_numa_compare(struct task_numa_env *env,
> >  		goto unlock;
> >  
> >  	if (!cur) {
> > -		if (maymove || imp > env->best_imp)
> > +		if (maymove)
> >  			goto assign;
> >  		else
> >  			goto unlock;
> 
> Srikar's patch here:
> 
>   http://lkml.kernel.org/r/1533276841-16341-4-git-send-email-srikar@linux.vnet.ibm.com
> 
> Also frobs this condition, but in a less radical way. Does that yield
> similar results?

I can check. I do wonder of course if the less radical approach just means
that automatic NUMA balancing and the load balancer simply disagree about
placement at a different time. It'll take a few days to have an answer as
the battery of workloads to check this take ages.

-- 
Mel Gorman
SUSE Labs