Hello James, There is some condition to meet to race-to-idle is valid. You may refer to a paper called "Critical Power Slope". It theoratically calculate whether higher frequency with longer idle is better or vice versa.
Thanks, Owen -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Bruno Girin Sent: Tuesday, January 06, 2009 3:10 AM To: James Cc: [email protected] Subject: Re: [Discuss] cpufreq governor and "race-to-idle" James, It all depends what you're doing on your system and whether the software you are using is typically CPU hungry. Most common desktop apps are not limited by the CPU. For instance, a browser like Firefox will typically spend more time waiting on disk and network IO than waiting on the CPU. So there's no point in the governor upping the CPU frequency if that doesn't help getting the job done faster. For example: my laptop, configured to use the OnDemand governor, spends most of its time in the lowest P-State at 800MHz, even when I am actively using it. That's because my definition of active is something like writing a document, a task for which the computer will need a variety or processing, disk IO, memory access, etc. That doesn't necessarilly stress the CPU (even if it stresses me!). However, if I do some photo manipulation using Image Magick on a large file (say 10+ mega-pixel), the CPU immediately jumps to its highest P-State (in its particular case running at 1.70GHz) because it is a very CPU intensive task and requires very little IO until the moment when it writes the resulting image to disk. Once it's finished, it returns to its 800MHz P-State. Other tasks will similarly get the CPU to change to an intermediary P-State (@ e.g. 1.2GHz) if that particular task can't be performed efficiently at 800MHz but does enough IO and other things that going above 1.2GHz would not help. Starting Firefox is an example. In your example, with a dual-core system, you'll probably find that you don't need to get out of the 800 MHz state very often because most of the tasks you do are blocking on other resources than CPU (disk or network IO being the likely culprits). If you want to stress your CPU a bit and see how your system responds, take a nice large JPEG, install Image Magick and run a command like: $ convert <input_file> -median 3 <output_file> Bruno 2008/9/10 James <[email protected]>: > Hi, > > I've noticed something with my system (kernel 2.6.25.11) that seems odd. > If I understood > the docs on the web page, the cpufreq governor should be doing > "race-to-idle": running at > full speed so as to get to idle faster. However, the processor's a Core2 > Duo at 2.2 GHz, > but /proc/cpuinfo says it's running at 800 MHz, and powertop says it's > spending its running > time in an 800 MHz P-state. > > Have I missed something? > > Thanks, > James > > _______________________________________________ > Discuss mailing list > [email protected] > http://mail.lesswatts.org/mailman/listinfo/discuss > _______________________________________________ Discuss mailing list [email protected] http://mail.lesswatts.org/mailman/listinfo/discuss _______________________________________________ Discuss mailing list [email protected] http://mail.lesswatts.org/mailman/listinfo/discuss
