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: <20180907124432.GN24082@hirez.programming.kicks-ass.net>
Date:   Fri, 7 Sep 2018 14:44:32 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mel Gorman <mgorman@...hsingularity.net>
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 01:37:39PM +0100, Mel Gorman wrote:
> 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.

Yeah, I was afraid it would.. Srikar, can you also evaluate, I suspect
we'll have to pick one of these two patches.