From mboxrd@z Thu Jan 1 00:00:00 1970 From: nicolas.pitre@linaro.org (Nicolas Pitre) Date: Thu, 7 Mar 2013 17:56:58 +0800 (HKT) Subject: [PATCH 00/16] big.LITTLE low-level CPU and cluster power management In-Reply-To: <20130307094017.GA6337@amd.pavel.ucw.cz> References: <1357777251-13541-1-git-send-email-nicolas.pitre@linaro.org> <20130307082721.GB28982@xo-6d-61-c0.localdomain> <20130307094017.GA6337@amd.pavel.ucw.cz> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, 7 Mar 2013, Pavel Machek wrote: > Hi! > > > > > Review comments are welcome! > > > > > > > > [*] General design information on the b.L switcher can be found here: > > > > http://lwn.net/Articles/481055/ > > > > However the code is only accessible to Linaro members for the > > > > time being. > > > > > > Assuming the lwn article is accurate: > > > > > > Hmm. So we have hw capable of running 8 cores, and then we introduce strange > > > switching code, because "scheduler is not ready". Sounds like a bad idea. > > > > > > I'd say: > > > > > > * expose all 8 cores. > > > > You may do that now. However the resulting power efficiency is far from > > optimal. > > Really? Assuming the lwn article is accurate, it will be exactly the > same. > > I propose exposing all 8 cores, then keeping 4 of them offline in > normal operation. This should have characteristics of your solution, > except that cpu does not change unexpectedly under the pinned tasks. > > > > * as long as scheduler is not ready, you can offline "the other" set of cores... > > > /sys/.../cpu/..../online > > > > You may do that now also. But system performance is far from optimal. > > Really? Do the offlining from the cpufreq code, and solution will be > equivalent to yours, except the hacks. No it is not equivalent. Offlining a CPU is a fairly heavy operation in Linux and you don't want to do that multiple times per second for example. Whereas the switcher "hack" is similar to a context switch in terms of software complexity. Nicolas