linux-kernel - Re: [PATCH -v2 04/18] sched/fair: Remove se->load.weight from se->avg.load

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Message-ID: <20170929152607.GC16286@e105550-lin.cambridge.arm.com>
Date:   Fri, 29 Sep 2017 16:26:10 +0100
From:   Morten Rasmussen <morten.rasmussen@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org, tj@...nel.org,
        josef@...icpanda.com, torvalds@...ux-foundation.org,
        vincent.guittot@...aro.org, efault@....de, pjt@...gle.com,
        clm@...com, dietmar.eggemann@....com, bsegall@...gle.com,
        yuyang.du@...el.com
Subject: Re: [PATCH -v2 04/18] sched/fair: Remove se->load.weight from
 se->avg.load_sum

On Fri, Sep 01, 2017 at 03:21:03PM +0200, Peter Zijlstra wrote:
> +/*
> + * sched_entity:
> + *
> + *   load_sum := runnable_sum
> + *   load_avg = se_weight(se) * runnable_avg
> + *
> + * cfq_rs:

I think this should be "cfs_rq" instead.

> + *
> + *   load_sum = \Sum se_weight(se) * se->avg.load_sum
> + *   load_avg = \Sum se->avg.load_avg
> + */

I find it a bit confusing that load_sum and load_avg have different
definitions, but I guess I will discover why dropping weight from
se->avg.load_sum helps a bit later. We can't do the same for cfs_rq as
it is a \Sum of sums where we add/remove contributions when tasks
migrate.

Have we defined the relation between runnable_sum and runnable_avg in a
comment somewhere already? Otherwise it might be helpful to add. It is
in the code of course :-)