From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mark Rutland Subject: Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity bindings Date: Tue, 15 Dec 2015 18:10:03 +0000 Message-ID: <20151215181002.GA8568@leverpostej> References: <20151214123616.GC3308@e106622-lin> <20151214165928.GV5727@sirena.org.uk> <20151215122238.GG16007@e106622-lin> <20151215133951.GY5727@sirena.org.uk> <20151215140135.GI31299@leverpostej> <20151215150813.GZ5727@sirena.org.uk> <20151215153218.GA7228@leverpostej> <20151215171713.GA5727@sirena.org.uk> <20151215172837.GD8012@leverpostej> <20151215174516.GB5727@sirena.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20151215174516.GB5727@sirena.org.uk> Sender: linux-kernel-owner@vger.kernel.org To: Mark Brown Cc: Juri Lelli , Rob Herring , linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org, peterz@infradead.org, vincent.guittot@linaro.org, linux@arm.linux.org.uk, sudeep.holla@arm.com, lorenzo.pieralisi@arm.com, catalin.marinas@arm.com, will.deacon@arm.com, morten.rasmussen@arm.com, dietmar.eggemann@arm.com, Pawel Moll , Ian Campbell , Kumar Gala , Maxime Ripard , Olof Johansson , Gregory CLEMENT , Paul Walmsley , Linus Walleij , Chen-Yu Tsai , Thomas Petazzoni List-Id: devicetree@vger.kernel.org On Tue, Dec 15, 2015 at 05:45:16PM +0000, Mark Brown wrote: > On Tue, Dec 15, 2015 at 05:28:37PM +0000, Mark Rutland wrote: > > On Tue, Dec 15, 2015 at 05:17:13PM +0000, Mark Brown wrote: > > > > Obviously people are going to get upset if we introduce performance > > > regressions - but that's true always, we can also introduce problems > > > with numbers people have put in DT. It seems like it'd be harder to > > > manage regressions due to externally provided magic numbers since > > > there's inherently less information there. > > > It's certainly still possible to have regressions in that case. Those > > regressions would be due to code changes in the kernel, given the DT > > didn't change. > > > I'm not sure I follow w.r.t. "inherently less information", unless you > > mean trying to debug without access to that DTB? > > If what the kernel knows about the system is that it's got a bunch of > cores with numbers assigned to them then all it's really got is those > numbers. If something changes that causes problems for some systems > (eg, because the numbers have been picked poorly but in a way that > happened to work well with the old code) that's not a lot to go on, the > more we know about the system the more likely it is that we'll be able > to adjust the assumptions in whatever new thing we do that causes > problems for any particular systems where we run into trouble. Regardless of where the numbers live (DT or kernel), all we have are numbers. I can see that changing the in-kernel numbers would be possible when modifyign the DT is not, but I don't see how that gives you more information. Mark.