linux-kernel - Re: [RFC PATCH 02/16] sched: Introduce CONFIG_SCHED

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Date:	Tue, 10 Jun 2014 11:06:41 +0100
From:	Morten Rasmussen <morten.rasmussen@....com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Henrik Austad <henrik@...tad.us>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	"vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
	"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
	"preeti@...ux.vnet.ibm.com" <preeti@...ux.vnet.ibm.com>,
	Dietmar Eggemann <Dietmar.Eggemann@....com>
Subject: Re: [RFC PATCH 02/16] sched: Introduce CONFIG_SCHED_ENERGY

On Tue, Jun 10, 2014 at 10:39:43AM +0100, Peter Zijlstra wrote:
> On Mon, Jun 09, 2014 at 11:20:27AM +0100, Morten Rasmussen wrote:
> > On Sun, Jun 08, 2014 at 07:03:16AM +0100, Henrik Austad wrote:
> > > On Fri, May 23, 2014 at 07:16:29PM +0100, Morten Rasmussen wrote:
> > > > The Energy-aware scheduler implementation is guarded by
> > > > CONFIG_SCHED_ENERGY.
> > > > 
> > > > Signed-off-by: Dietmar Eggemann <dietmar.eggemann@....com>
> > > > Signed-off-by: Morten Rasmussen <morten.rasmussen@....com>
> > > > ---
> > > >  arch/arm/Kconfig |    5 +++++
> > > >  1 file changed, 5 insertions(+)
> > > > 
> > > > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> > > > index ab438cb..bfc3a85 100644
> > > > --- a/arch/arm/Kconfig
> > > > +++ b/arch/arm/Kconfig
> > > 
> > > Is this going to be duplicate for each architecture enabling this? Why
> > > not make a kernel/Kconfig.energy and link to that from those
> > > architectures using it?
> > 
> > kernel/Kconfig.energy is better I think.
> 
> Well, strictly speaking I'd prefer to not have more sched CONFIG knobs.
> 
> Do we really need to have this CONFIG guarded?

How would you like to disable the energy stuff for users for whom
latency is everything?

I mean, we are adding some extra load/utilization tracking. While I
think we should do everything possible to minimize the overhead, I think
it is unrealistic to assume that it will be zero. Is a some extra 'if
(energy_enabled)' acceptable?

I'm open for other suggestions.
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