linux-kernel - Re: [PATCH v4 05/11] sched/fair: use rq->nr

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Message-ID: <20191030155424.GK3016@techsingularity.net>
Date:   Wed, 30 Oct 2019 15:54:24 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     linux-kernel@...r.kernel.org, mingo@...hat.com,
        peterz@...radead.org, pauld@...hat.com, valentin.schneider@....com,
        srikar@...ux.vnet.ibm.com, quentin.perret@....com,
        dietmar.eggemann@....com, Morten.Rasmussen@....com,
        hdanton@...a.com, parth@...ux.ibm.com, riel@...riel.com
Subject: Re: [PATCH v4 05/11] sched/fair: use rq->nr_running when balancing
 load

On Fri, Oct 18, 2019 at 03:26:32PM +0200, Vincent Guittot wrote:
> cfs load_balance only takes care of CFS tasks whereas CPUs can be used by
> other scheduling class. Typically, a CFS task preempted by a RT or deadline
> task will not get a chance to be pulled on another CPU because the
> load_balance doesn't take into account tasks from other classes.
> Add sum of nr_running in the statistics and use it to detect such
> situation.
> 
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>

Patch is ok but it'll be easier in the future to mix up sum_nr_running
and sum_h_nr_running in the future. Might be best to make sum_nr_running
sum_any_running and the hierarchy one sum_cfs_running. I don't feel
strongly either way, because it's almost certainly due to the fact I
almost never care about non-cfs tasks when thinking about the scheduler.

-- 
Mel Gorman
SUSE Labs