linux-kernel - Re: [PATCH V5 0/5] Queue work on power efficient wq

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Message-ID: <20130708185509.GH29556@pengutronix.de>
Date:	Mon, 8 Jul 2013 20:55:09 +0200
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	tj@...nel.org, davem@...emloft.net, airlied@...hat.com,
	axboe@...nel.dk, tglx@...utronix.de, peterz@...radead.org,
	mingo@...hat.com, rostedt@...dmis.org,
	linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	robin.randhawa@....com, Steve.Bannister@....com, Livi@...per.es
Subject: Re: [PATCH V5 0/5] Queue work on power efficient wq

Hello,

On Mon, Jul 08, 2013 at 10:18:08PM +0530, Viresh Kumar wrote:
> On 8 July 2013 21:27, Uwe Kleine-König <u.kleine-koenig@...gutronix.de> wrote:
> > On Mon, Jul 08, 2013 at 09:17:01PM +0530, Viresh Kumar wrote:
> 
> >> Well, big LITTLE still runs an SMP kernel :) and so has this flag set.
> > The 'S' is justified because cpu0 and cpu1 are of the same type? Are
> > there b.L systems that have only one big and one LITTLE cpu? Do these
> > use SMP, too?
> 
> Following definition of SMP says:
> http://en.wikipedia.org/wiki/Symmetric_Multiprocessor
> 
> A system is SMP when:
> - It has same type of cores
> - controlled by a single instance of OS.
> 
> In big LITTLE first one is obviously not completely true as you pointed out.
> But second one is and so I would say its an SMP system :)
> 
> Don't know how it should be called though.
MP maybe.

> >> You can make it dependent on that if required.
> > Well, it's not required. It's just that the corresponding question in
> > make oldconfig isn't really an enrichment for a kernel targeting an
> > Cortex M3 :-)
> 
> Just to make it clear enough, you are saying it doesn't make any
> sense to enable it for M3? But because it is disabled by default,
> the problem is not seen?
No I'm saying that asking me is bad because on an UP machine it won't
matter what I answer. So please don't ask me if SMP is off.

> Why? Can't we have two M3's on a SoC and run an SMP kernel over
> it?
Yeah, you can. Then you'd have SMP (or MP) enabled though and the choice
for that workqueue thing makes a difference. In that case asking is OK.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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