linux-kernel - Re: [PATCH 04/14] sched: SCHED_DEADLINE SMP-related data structures & logic.

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Message-ID: <20131014120306.GH3081@twins.programming.kicks-ass.net>
Date:	Mon, 14 Oct 2013 14:03:06 +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 04/14] sched: SCHED_DEADLINE SMP-related data structures
 & logic.

On Mon, Oct 14, 2013 at 12:43:36PM +0200, Juri Lelli wrote:
> +static inline void dl_set_overload(struct rq *rq)
> +{
> +	if (!rq->online)
> +		return;
> +
> +	cpumask_set_cpu(rq->cpu, rq->rd->dlo_mask);
> +	/*
> +	 * Must be visible before the overload count is
> +	 * set (as in sched_rt.c).
> +	 */
> +	wmb();
> +	atomic_inc(&rq->rd->dlo_count);
> +}

Please, make that smp_wmb() and modify the comment to point to the
matching barrier ; I couldn't find one! Which suggests something is
amiss.

Ideally we'd have something like smp_wmb__after_set_bit() but alas.
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