linux-kernel - Re: [RFC][PATCH 02/11] sched: SCHED

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Date:	Tue, 13 Apr 2010 20:22:17 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Raistlin <raistlin@...ux.it>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Chris Friesen <cfriesen@...tel.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Darren Hart <darren@...art.com>,
	Henrik Austad <henrik@...tad.us>,
	Johan Eker <johan.eker@...csson.com>,
	"p.faure" <p.faure@...tech.ch>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Claudio Scordino <claudio@...dence.eu.com>,
	michael trimarchi <trimarchi@...is.sssup.it>,
	Fabio Checconi <fabio@...dalf.sssup.it>,
	Tommaso Cucinotta <t.cucinotta@...up.it>,
	Juri Lelli <juri.lelli@...il.com>,
	Nicola Manica <nicola.manica@...il.com>,
	Luca Abeni <luca.abeni@...tn.it>
Subject: Re: [RFC][PATCH 02/11] sched: SCHED_DEADLINE policy implementation.

On Sun, 2010-02-28 at 20:17 +0100, Raistlin wrote:
> +/*
> + * When a -deadline task is queued back on the runqueue, its runtime and
> + * deadline might need updating.
> + *
> + * The policy here is that we update the deadline of the task only if:
> + *  - the current deadline is in the past,
> + *  - using the remaining remaining with the current deadline would make

"remaining runtime", I presume?

> + *    the task exceed its bandwidth.
> + */
> +static void update_dl_entity(struct sched_dl_entity *dl_se)
> +{
> +       struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
> +       struct rq *rq = rq_of_dl_rq(dl_rq);
> +
> +       /*
> +        * The arrival of a new task (or of a new task instance) needs
> +        * special treatment. The actual scheduling parameters have to be
> +        * "renewed" instead of recalculatetd accordingly to the bandwidth
> +        * enforcement rule.
> +        */
> +       if (dl_se->flags & DL_NEW) {
> +               setup_new_dl_entity(dl_se);
> +               return;
> +       }
> +
> +       if (dl_time_before(dl_se->deadline, rq->clock))
> +               goto update;
> +
> +       if (!dl_check_bandwidth(dl_se, rq->clock)) {
> +update:
> +               dl_se->deadline = rq->clock + dl_se->dl_deadline;
> +               dl_se->runtime = dl_se->dl_runtime;
> +       }
> +} 

We could write that as:

  if (dl_time_before(dl_se, rq->clock) ||
      !dl_check_bandwidth(dl_se, rq->clock)) {
	/* reset parameters */
  }

Also, I was wondering about a more descriptive name for
dl_check_bandwidth(), check _what_ about the bandwidth!?

dl_bandwidth_overflow() perhaps, that would also remove that negation.
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