linux-kernel - Re: [RFC 2/4] sched/numa: replace runnable_load_avg by load

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Message-ID: <20200213151430.GY3466@techsingularity.net>
Date:   Thu, 13 Feb 2020 15:14:30 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Phil Auld <pauld@...hat.com>
Cc:     Hillf Danton <hdanton@...a.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Parth Shah <parth@...ux.ibm.com>,
        Valentin Schneider <valentin.schneider@....com>
Subject: Re: [RFC 2/4] sched/numa: replace runnable_load_avg by load_avg

On Thu, Feb 13, 2020 at 10:00:26AM -0500, Phil Auld wrote:
> On Thu, Feb 13, 2020 at 01:46:55PM +0000 Mel Gorman wrote:
> > On Thu, Feb 13, 2020 at 09:16:58PM +0800, Hillf Danton wrote:
> > > > -	load = task_h_load(env->p);
> > > > -	dst_load = env->dst_stats.load + load;
> > > > -	src_load = env->src_stats.load - load;
> > > > -
> > > >  	/*
> > > > -	 * If the improvement from just moving env->p direction is better
> > > > -	 * than swapping tasks around, check if a move is possible.
> > > > +	 * If dst node has spare capacity, then check if there is an
> > > > +	 * imbalance that would be overruled by the load balancer.
> > > >  	 */
> > > > -	maymove = !load_too_imbalanced(src_load, dst_load, env);
> > > > +	if (env->dst_stats.node_type == node_has_spare) {
> > > > +		unsigned int imbalance;
> > > > +		int src_running, dst_running;
> > > > +
> > > > +		/* Would movement cause an imbalance? */
> > > > +		src_running = env->src_stats.nr_running - 1;
> > > > +		dst_running = env->src_stats.nr_running + 1;
> > > > +		imbalance = max(0, dst_running - src_running);
> > > 
> > > Have trouble working out why 2 is magician again to make your test data nicer :P
> > > 
> > 
> > This is calculating what the nr_running would be after the move and
> > checking if an imbalance exists after the move forcing the load balancer
> > to intervene.
> 
> Isn't that always going to work out to 2? 
> 

Crap, stupid cut and paste moving between source trees. Yes, this is
broken.

-- 
Mel Gorman
SUSE Labs