linux-kernel - Re: [PATCH 09/13] sched: Add bandwidth management for sched

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Date:	Fri, 20 Dec 2013 18:29:46 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	tglx@...utronix.de, mingo@...hat.com, 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,
	juri.lelli@...il.com, 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
Subject: Re: [PATCH 09/13] sched: Add bandwidth management for sched_dl

On Fri, 20 Dec 2013 22:44:13 +0100
Peter Zijlstra <peterz@...radead.org> wrote:


> @@ -5056,10 +5018,28 @@ static int sched_cpu_inactive(struct not
>  	switch (action & ~CPU_TASKS_FROZEN) {
>  	case CPU_DOWN_PREPARE:
>  		set_cpu_active((long)hcpu, false);
> -		return NOTIFY_OK;
> -	default:
> -		return NOTIFY_DONE;
> +		break;
>  	}
> +
> +	switch (action) {
> +	case CPU_DOWN_PREPARE: /* explicitly allow suspend */

Instead of the double switch (which is quite confusing), what about
just adding:

	if (!(action & CPU_TASKS_FROZEN))

I mean, the above switch gets called for both cases, this only gets
called for the one case. This case is a subset of the above. I don't
see why an if () would not be better than a double (confusing) switch().

Also, it seems that this change also does not return NOTIFY_DONE if
something other than CPU_DOWN_PREPARE is passed in.

-- Steve

> +		{
> +			struct dl_bw *dl_b = dl_bw_of(cpu);
> +			bool overflow;
> +			int cpus;
> +
> +			raw_spin_lock_irqsave(&dl_b->lock, flags);
> +		       	cpus = dl_bw_cpus(cpu);
> +			overflow = __dl_overflow(dl_b, cpus, 0, 0);
> +			raw_spin_unlock_irqrestore(&dl_b->lock, flags);
> +
> +			if (overflow)
> +				return notifier_from_errno(-EBUSY);
> +		}
> +		break;
> +	}
> +
> +	return NOTIFY_OK;
>  }
>  
>  static int __init migration_init(void)

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