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

From: Pavel Machek
Date: Sun Jul 31 2005 - 16:12:20 EST


> >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.

Then the second test was probably flawed, possibly because we have
some more work to do. No display is irrelevant, HZ=100 will still save
0.5W with running display. Spinning disk also does not produce CPU
load (and we *will* want to have disk spinned down). No daemons... if
some daemon wakes every msec, we want to fix the daemon.

> 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
> Last I checked, ACPI and CPU speed scaling were not enabled by default;

Kernel defaults are irelevant; distros change them anyway. [But we
probably want to enable ACPI and cpufreq by default, because that
matches what 99% of users will use.]

> 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 really don't think default HZ in kernel config is such a big
deal. You'll want to support HZ=100 on 2.6.X, anyway...

> 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

defconfig on i386 is Linus' configuration. Maybe server-config and
laptop-config would be good idea...
if you have sharp zaurus hardware you don't need... you know my address
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