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

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Date:	Sat, 21 Dec 2013 11:05:00 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Steven Rostedt <rostedt@...dmis.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, Dec 20, 2013 at 06:29:46PM -0500, Steven Rostedt wrote:
> 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().

I don't see the confusion in the double switch(), but sure an if would
work too I suppose.

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

Yeah, I had a look but couldn't find an actual difference between
NOTIFY_DONE and NOTIFY_OK. Maybe I missed it..
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