From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pavel Machek Subject: cpufreq terminally broken [was Re: community PM requirements/issues and PowerOP] Date: Tue, 12 Sep 2006 00:56:17 +0200 Message-ID: <20060911225617.GB13474@elf.ucw.cz> References: <450516E8.9010403@gmail.com> <20060911082025.GD1898@elf.ucw.cz> <20060911195546.GB11901@elf.ucw.cz> <4505CCDA.8020501@gmail.com> <20060911210026.GG11901@elf.ucw.cz> <4505DDA6.8080603@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: Content-Disposition: inline In-Reply-To: <4505DDA6.8080603@gmail.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-pm-bounces@lists.osdl.org Errors-To: linux-pm-bounces@lists.osdl.org To: kernel list , "Eugeny S. Mints" Cc: pm list , Preece Scott-PREECE List-Id: linux-pm@vger.kernel.org Hi! Just for the record... this goes out to the lkml. This discussion was internal for way too long. (for interested lkml readers, I'm sure linux-pm mailing list has public archive somewhere). On Tue 2006-09-12 02:05:26, Eugeny S. Mints wrote: > Pavel Machek wrote: > >>>>- PowerOP is only one layer (towards the bottom) in a power managemen= t = > >>>>solution. > >>>>- PowerOP does *not* replace cpufreq > >>>PowerOP provides userland interface for changing processor > >>>frequency. That's bad -- duplicate interface. > >>Basically the biggest problem with cpufreq interface is that cpufreq ha= s = > >>"chose > >>predefined closest to a given frequency" functionality implemented in t= he > >>kernel while there is _no_ any reason to have this functionality = > >>implemented in > >>the kernel if we have sysfs interface exported by PowerOP in place - yo= u = > >>just > > > >No, there is reason to keep that in kernel -- so that cpufreq > >userspace interface can be kept, and so that resulting kernel<->user > >interface is not ugly. > Cpuferq defines cpufreq_frequency_table structure in arch independent = > header while it's arch dependent data structure. A lot of code is built = > around this invalid basic brick and therefore is invalid: cpufreq tables, = > interface with cpu freq drivers, etc. Notion of transition latency as it = > defined by cpufreq is wrong because it's not a function of cpu type but = > function of current and next operating point. no runtime control on = > operating points set. it's always the same set of operating points for al= l = > system cpus in smp case and no way to define different sets or track any = > dependencies in case say multi core cpus. insufficient kernel<->user spac= e = > interface to handle embedded requirements and no way to extend it within = > current design. Shall I continue? Why should then anyone want to keep = > cpufreq userspace interface just due to keep it? Yes, please continue. I do not think we can just rip cpufreq interface out of kernel, and I do not think it is as broken as you claim it is. Ripping interface out of kernel takes years. I'm sure cpufreq_frequency_table could be moved to asm/ header if you felt strongly about that. I believe we need to fix cpufreq if it is broken for embedded cases. Pavel -- = (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blo= g.html