Hi! > To save energy, the higher frequencies should be avoided and only used > when the application performance requirements can not be satisfied > otherwise (e.g. spread tasks across more cpus if possible).
I argue this is untrue for any task where user waits for its completion with screen on. (And that's quite important subset). Lets take Nokia n900 as an example. (source http://wiki.maemo.org/N900_Hardware_Power_Consumption) Sleeping CPU: 2mA Screen on: 230mA CPU loaded: 250mA Now, lets believe your numbers and pretend system can operate at 33% of speed with 11% power consumption. Lets take task that takes 10 seconds on max frequency: ~ 10s * 470mA = 4700mAs You suggest running at 33% speed, instead; that means 30 seconds on low requency. CPU on low: 25mA (assumed). ~ 30s * 255mA = 7650mAs Hmm. So race to idle is good thing on Intel machines, and it is good thing on ARM design I have access to. And you even acknowledge it here, right: > When considering the total system power it may save energy in some > scenarios by running the cpu faster to allow other power hungry parts of > the system to be shut down faster. However, this is highly platform and > application dependent. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
