Re: Power consumption HZ100, HZ250, HZ1000: new numbers

From: James Bruce
Date: Sun Jul 31 2005 - 15:23:37 EST

Pavel Machek wrote:
First numbers were 0.5W on idle system; that shows what kind of
powersaving can be done. Powersaving is no longer possible when artsd
is not running, but that should not be used as argument against it.

It was an idle system with no display, zero daemons running, and the hard drive off. In other words, a machine that nobody could use which might as well be hibrinating. While it was an important test to find out the most one could hope to save, its unrealistic for an actual usage case. The later test was more realistic, and not suprisingly showed quite a bit less power savings.

I really like having 250HZ as an _option_, but what I don't see is why it should be the _default_. I believe this is Lee's position as well. Last I checked, ACPI and CPU speed scaling were not enabled by default; If users are willing to change all those other options, why can't we expect them to select 250HZ/100HZ? Instead, we are quadrupling latency for desktop users (for little or no power savings), just so that laptop users can save enabling one option out of the many they already need to change.

I have a fixed-framerate app that had to busywait in the days of 2.4.x. It was nice in 2.6.x to not have to busywait, but with 250HZ that code will be coming back again. And unfortunately this app can't be made variable-framerate, as it is simulating video hardware. The same goes for apps playing movies/animations; Sometimes programs just need a semi-accurate sleep, and can't demand root priveledges to get it.

I remember that 1000HZ was chosen in part so that fewer people would complain about the need for the Posix highres timers. Well now that 1000HZ is going away, can we have our highres timers or not? My guess is no. Thus we've predictably come back out here to complain. All we're asking is that the default value be left alone until tick-skipping approaches and/or highres timers are given a chance to work. That way we can see if we can find a solution that truly makes everyone happy.

In a sense I feel this whole thing boils down to the fact that we don't have something like "make laptop-config" and "make server-config". I'm glad we could save 5.2% of the power for a laptop user by changing the defaults (as long as you remember to change other options too). However I'm not sure it should come at the expense of those doing video or audio on a desktop. Right now with the one-size-fits-all defaults, we end up having to make that tradeoff.

- Jim Bruce
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