From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751500AbaFJLWU (ORCPT ); Tue, 10 Jun 2014 07:22:20 -0400 Received: from mail-la0-f43.google.com ([209.85.215.43]:43671 "EHLO mail-la0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750979AbaFJLWS (ORCPT ); Tue, 10 Jun 2014 07:22:18 -0400 Date: Tue, 10 Jun 2014 13:17:32 +0200 From: Henrik Austad To: Peter Zijlstra Cc: Morten Rasmussen , "linux-kernel@vger.kernel.org" , "linux-pm@vger.kernel.org" , "mingo@kernel.org" , "rjw@rjwysocki.net" , "vincent.guittot@linaro.org" , "daniel.lezcano@linaro.org" , "preeti@linux.vnet.ibm.com" , Dietmar Eggemann Subject: Re: [RFC PATCH 02/16] sched: Introduce CONFIG_SCHED_ENERGY Message-ID: <20140610111732.GA30139@austad.us> References: <1400869003-27769-1-git-send-email-morten.rasmussen@arm.com> <1400869003-27769-3-git-send-email-morten.rasmussen@arm.com> <20140608060316.GA18179@austad.us> <20140609102027.GA29593@e103034-lin> <20140610093943.GA6758@twins.programming.kicks-ass.net> <20140610100641.GB1581@e103034-lin> <20140610102353.GC6758@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140610102353.GC6758@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 10, 2014 at 12:23:53PM +0200, Peter Zijlstra wrote: > 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. Isn't this asking for trouble? I do get the point of not introducing more make-ifdeffery, but I'm not so sure the alternative is much better. Do we really want to spend time tracing down bugs introduced via a self-modifying process in something as central as the scheduler? > 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. True, but if that is the argument, how is adding this as a dynamic thing any better, you still end up with a test-matrix of the same size? Building a kernel isn't _that_ much work and it would make the test-scripts all the much simpler to maintain if we don't have to rely on some dynamic tweaking of the core. Just sayin' -- Henrik Austad