linux-kernel - Re: [PATCH 2/3 v2] sched/fair: don't set LBF_ALL

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Date:   Mon, 11 Jan 2021 15:42:26 +0000
From:   Mel Gorman <mgorman@...e.de>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        bristot@...hat.com, valentin.schneider@....com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3 v2] sched/fair: don't set LBF_ALL_PINNED unnecessarily

On Thu, Jan 07, 2021 at 11:33:24AM +0100, Vincent Guittot wrote:
> Setting LBF_ALL_PINNED during active load balance is only valid when there
> is only 1 running task on the rq otherwise this ends up increasing the
> balance interval whereas other tasks could migrate after the next interval
> once they become cache-cold as an example.
> 
> LBF_ALL_PINNED flag is now always set it by default. It is then cleared
> when we find one task that can be pulled when calling detach_tasks() or
> during active migration.
> 
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>

When reviewing this, I found it curious that sched_nr_migrate_break is
a const instead of a #define. It's not clear why as it only appears to
exist in case sysctl_sched_nr_migrate is set higher than 32 to prevent
rq lock starvation.

With your patch, s/atleast/at least/ in the comments if there is another
version.

Otherwise, I didn't spot a real problem so

Acked-by: Mel Gorman <mgorman@...e.de>

-- 
Mel Gorman
SUSE Labs