linux-kernel - Re: [PATCH 2/2] sched/fair: Always propagate runnable_load

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Date:   Tue, 2 May 2017 18:37:43 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mike Galbraith <efault@....de>, Paul Turner <pjt@...gle.com>,
        Chris Mason <clm@...com>, kernel-team@...com
Subject: Re: [PATCH 2/2] sched/fair: Always propagate runnable_load_avg

Hello, Vincent.

On Tue, May 02, 2017 at 03:26:12PM +0200, Vincent Guittot wrote:
> > IMHO, we should better improve load balance selection. I'm going to
> > add smarter group selection in load_balance. that's something we
> > should have already done but it was difficult without load/util_avg
> > propagation. it should be doable now
> 
> Could you test the patch in load_balance below ?
> If group is not overloaded which means that threads have all runtime they
> want, we select the cfs_rq according to the number of running threads instead

So, this didn't help.  Tried also w/ return true added on the else
clause but that didn't help either.

Anyways, once debugged, the idea would work for this particular test
case and in general we should avoid picking a CPU as the busiest if it
doesn't have extra threads to give away; however, this isn't the
proper fix for the identified problem and basing load balancing soley
on the number of tasks is far more likely to be harmful than the other
way around.

Thanks.

-- 
tejun