linux-kernel - Re: [PATCH v4 06/11] sched/fair: use load instead of runnable load in load

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Message-ID: <20191030155829.GL3016@techsingularity.net>
Date:   Wed, 30 Oct 2019 15:58:29 +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 06/11] sched/fair: use load instead of runnable load
 in load_balance

On Fri, Oct 18, 2019 at 03:26:33PM +0200, Vincent Guittot wrote:
> runnable load has been introduced to take into account the case
> where blocked load biases the load balance decision which was selecting
> underutilized group with huge blocked load whereas other groups were
> overloaded.
> 
> The load is now only used when groups are overloaded. In this case,
> it's worth being conservative and taking into account the sleeping
> tasks that might wakeup on the cpu.
> 
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>

Hmm.... ok. Superficially I get what you're doing but worry slightly
about groups that have lots of tasks that are frequently idling on short
periods of IO.

Unfortuntely when I queued this series for testing I did not queue a load
that idles rapidly for short durations that would highlight problems in
that area.

I cannot convince myself it's ok enough for an ack but I have no reason
to complain either.

-- 
Mel Gorman
SUSE Labs