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

From: James Bruce
Date: Sun Jul 31 2005 - 17:16:40 EST

Pavel Machek wrote:
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 was talking about percentage saved; That 5.2% easily drops below 2% once other things start sucking up power. I was thinking that way since the percentage saved is what determines the overall battery life increase. You're right in that the absolute power draw difference should stay the same, and that seems to be the case is Marc's tests (ignoring the brokenness of artsd).

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.]

True, but I think a lot of distros treat the values as recommendations. I guess we'll find out what they do with this option soon enough.

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...

Yeah, but if its only the default value for servers and laptops they won't normally be running my app. I'll be truly happy the day I can delete all the busy-waiting code, as I think its about the ugliest workaround in modern computing.

defconfig on i386 is Linus' configuration. Maybe server-config and
laptop-config would be good idea...

Well maybe if we can get enough people who agree then it could happen. I think a "laptop-config" and "server-config" file could fit nicely into the current arch/*/config/ directory structure. I'm not sure how those defconfig files are kept up to date though.

- Jim
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