linux-kernel - Re: [RFC v5 2/9] sched/deadline: improve the tracking of active utilization

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Message-ID: <20170324223146.1bd4bba5@grimm.local.home>
Date:   Fri, 24 Mar 2017 22:31:46 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     luca abeni <luca.abeni@...tannapisa.it>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@....com>,
        Claudio Scordino <claudio@...dence.eu.com>,
        Tommaso Cucinotta <tommaso.cucinotta@...up.it>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>
Subject: Re: [RFC v5 2/9] sched/deadline: improve the tracking of active
 utilization

On Fri, 24 Mar 2017 22:47:15 +0100
luca abeni <luca.abeni@...tannapisa.it> wrote:

> Ok... Since I am not good at ascii art, would it be ok to add a textual
> description? If yes, I'll add a comment like:
> "
> The utilization of a task is added to the runqueue's active utilization
> when the task becomes active (is enqueued in the runqueue), and is
> removed when the task becomes inactive. A task does not become
> immediately inactive when it blocks, but becomes inactive at the so
> called "0 lag time"; so, we setup the "inactive timer" to fire at the
> "0 lag time". When the "inactive timer" fires, the task utilization is
> removed from the runqueue's active utilization. If the task wakes up
> again on the same runqueue before the "0 lag time", the active
> utilization must not be changed and the "inactive timer" must be
> cancelled. If the task wakes up again on a different runqueue before
> the "0 lag time", then the task's utilization must be removed from the
> previous runqueue's active utilization and must be added to the new
> runqueue's active utilization.
> In order to avoid races between a task waking up on a runqueue while the
> "inactive timer" is running on a different CPU, the "dl_non_contending"
> flag is used to indicate that a task is not on a runqueue but is active
> (so, the flag is set when the task blocks and is cleared when the
> "inactive timer" fires or when the task  wakes up).

Sure, the above is great if you never want anyone to read it ;)

Can you please break it up a little. My head starts to spin by the
third line down.

-- Steve

> "
> (if this is ok, where can I add this comment?)