linux-kernel - Re: [PATCH 03/14] sched,fair: redefine runnable_load_avg as the sum of task_h

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Date:   Mon, 29 Jul 2019 22:11:32 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Rik van Riel <riel@...riel.com>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com, pjt@...gle.com,
        dietmar.eggemann@....com, mingo@...hat.com,
        morten.rasmussen@....com, tglx@...utronix.de,
        mgorman@...hsingularity.net, vincent.guittot@...aro.org
Subject: Re: [PATCH 03/14] sched,fair: redefine runnable_load_avg as the sum
 of task_h_load

On Mon, Jul 22, 2019 at 01:33:37PM -0400, Rik van Riel wrote:
> The runnable_load magic is used to quickly propagate information about
> runnable tasks up the hierarchy of runqueues. The runnable_load_avg is
> mostly used for the load balancing code, which only examines the value at
> the root cfs_rq.
> 
> Redefine the root cfs_rq runnable_load_avg to be the sum of task_h_loads
> of the runnable tasks. This works because the hierarchical runnable_load of
> a task is already equal to the task_se_h_load today. This provides enough
> information to the load balancer.
> 
> The runnable_load_avg of the cgroup cfs_rqs does not appear to be
> used for anything, so don't bother calculating those.
> 
> This removes one of the things that the code currently traverses the
> cgroup hierarchy for, and getting rid of it brings us one step closer
> to a flat runqueue for the CPU controller.

Nice!