From mboxrd@z Thu Jan 1 00:00:00 1970 From: Henrik Austad Subject: Re: [RFC PATCH 02/16] sched: Introduce CONFIG_SCHED_ENERGY Date: Tue, 10 Jun 2014 13:17:32 +0200 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 Return-path: Received: from mail-lb0-f178.google.com ([209.85.217.178]:47094 "EHLO mail-lb0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750992AbaFJLWS (ORCPT ); Tue, 10 Jun 2014 07:22:18 -0400 Received: by mail-lb0-f178.google.com with SMTP id w7so3763088lbi.23 for ; Tue, 10 Jun 2014 04:22:16 -0700 (PDT) Content-Disposition: inline In-Reply-To: <20140610102353.GC6758@twins.programming.kicks-ass.net> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org 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 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