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

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Date:	Tue, 10 Jun 2014 12:23:53 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Morten Rasmussen <morten.rasmussen@....com>
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 11:06:41AM +0100, Morten Rasmussen wrote:
> 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.

We have the jump-label stuff to do self modifying code ;-) The only
thing we need to be careful with is data-layout.

So I'm _hoping_ we can do all this without more CONFIG knobs, because
{PREEMPT*SMP*CGROUP^3*NUMA^2} is already entirely annoying to
build and run test, not to mention that distro builds will have no other
option than to enable everything anyhow.

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