linux-kernel - Re: [PATCH v2 1/5] sched/fair: Reorder enqueue/dequeue_task

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Message-ID: <ee38d205-b356-9474-785e-e514d81b7d7f@arm.com>
Date:   Tue, 18 Feb 2020 13:37:37 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com, rostedt@...dmis.org,
        bsegall@...gle.com, mgorman@...e.de, linux-kernel@...r.kernel.org
Cc:     pauld@...hat.com, parth@...ux.ibm.com, valentin.schneider@....com,
        hdanton@...a.com
Subject: Re: [PATCH v2 1/5] sched/fair: Reorder enqueue/dequeue_task_fair path

On 14/02/2020 16:27, Vincent Guittot wrote:
> The walk through the cgroup hierarchy during the enqueue/dequeue of a task
> is split in 2 distinct parts for throttled cfs_rq without any added value
> but making code less readable.
> 
> Change the code ordering such that everything related to a cfs_rq
> (throttled or not) will be done in the same loop.
> 
> In addition, the same steps ordering is used when updating a cfs_rq:
> - update_load_avg
> - update_cfs_group
> - update *h_nr_running

Is this code change really necessary? You pay with two extra goto's. We
still have the two for_each_sched_entity(se)'s because of 'if
(se->on_rq); break;'.

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