linux-kernel - Re: [PATCH 03/14] sched: SCHED_DEADLINE structures & implementation.

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Message-ID: <20131014114433.GE3081@twins.programming.kicks-ass.net>
Date:	Mon, 14 Oct 2013 13:44:33 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Juri Lelli <juri.lelli@...il.com>
Cc:	tglx@...utronix.de, mingo@...hat.com, rostedt@...dmis.org,
	oleg@...hat.com, fweisbec@...il.com, darren@...art.com,
	johan.eker@...csson.com, p.faure@...tech.ch,
	linux-kernel@...r.kernel.org, claudio@...dence.eu.com,
	michael@...rulasolutions.com, fchecconi@...il.com,
	tommaso.cucinotta@...up.it, nicola.manica@...i.unitn.it,
	luca.abeni@...tn.it, dhaval.giani@...il.com, hgu1972@...il.com,
	paulmck@...ux.vnet.ibm.com, raistlin@...ux.it,
	insop.song@...il.com, liming.wang@...driver.com, jkacur@...hat.com,
	harald.gustafsson@...csson.com, vincent.guittot@...aro.org,
	bruce.ashfield@...driver.com--no-chain-reply-to
Subject: Re: [PATCH 03/14] sched: SCHED_DEADLINE structures & implementation.

On Mon, Oct 14, 2013 at 12:43:35PM +0200, Juri Lelli wrote:
> +static void update_curr_dl(struct rq *rq)
> +{
> +	struct task_struct *curr = rq->curr;
> +	struct sched_dl_entity *dl_se = &curr->dl;
> +	u64 delta_exec;
> +
> +	if (!dl_task(curr) || !on_dl_rq(dl_se))
> +		return;
> +
> +	/*
> +	 * Consumed budget is computed considering the time as
> +	 * observed by schedulable tasks (excluding time spent
> +	 * in hardirq context, etc.)
> +	 */
> +	delta_exec = rq->clock_task - curr->se.exec_start;

Oh, cute.. So we compute deadlines from rq->clock but compute runtime
from rq->clock_task.

So won't that give funny results in that clock_task is generally slower
than clock; so people get more 'time'.

Maybe there's some illumination on this point further on; I'll continue
reading.
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