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

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Message-ID: <525C18F2.9050205@gmail.com>
Date:	Mon, 14 Oct 2013 18:16:50 +0200
From:	Juri Lelli <juri.lelli@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
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
Subject: Re: [PATCH 03/14] sched: SCHED_DEADLINE structures & implementation.

On 10/14/2013 01:33 PM, Peter Zijlstra wrote:
> On Mon, Oct 14, 2013 at 12:43:35PM +0200, Juri Lelli wrote:
>> +static void replenish_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);
>> +
>> +	/*
>> +	 * We keep moving the deadline away until we get some
>> +	 * available runtime for the entity. This ensures correct
>> +	 * handling of situations where the runtime overrun is
>> +	 * arbitrary large.
>> +	 */
>> +	while (dl_se->runtime <= 0) {
>> +		dl_se->deadline += dl_se->dl_deadline;
>> +		dl_se->runtime += dl_se->dl_runtime;
>> +	}
> 
> Are we sure GCC won't be 'smart' and bite us; that is do we need
> something like:
> 
>   asm("" : "+rm" (dl_se->runtime));
> 
> in there? See:
> 
> 0d98bb2656e9 sched: Prevent compiler from optimising the sched_avg_update() loop
> 

When disassembled everything seems fine, at least for x86 and ARM. Do I add the
fake data hazard anyway?

Thanks,

- Juri
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