linux-kernel - Re: [RFC][PATCH v2] sched/rt: Use IPI to trigger RT task push migration instead of pulling

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Date:	Tue, 24 Feb 2015 16:23:39 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Clark Williams <williams@...hat.com>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Jörn Engel <joern@...estorage.com>
Subject: Re: [RFC][PATCH v2] sched/rt: Use IPI to trigger RT task push
 migration instead of pulling

On Tue, 24 Feb 2015 13:39:46 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> @@ -1775,6 +1946,15 @@ static int pull_rt_task(struct rq *this_
>  	 */
>  	smp_rmb();
>  
> +	/* Use local just in case a feature is switched in the middle of this */
> +	if ((use_ipi = sched_feat(RT_PUSH_IPI))) {
> +		/* Make sure the update to pending is visible here. */
> +		smp_rmb();

While porting this to the -rt kernel, I noticed that this rmb is
unneeded. It's already called above for a different reason :-p

-- Steve

> +
> +		/* If a push ipi is out, then we must do the old method */
> +		push_pending = READ_ONCE(this_rq->rt.push_csd_pending);
> +	}
> +
>  	for_each_cpu(cpu, this_rq->rd->rto_mask) {
>  		if (this_cpu == cpu)
>  			continue;
--
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