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Thread: the acpi_cpufreq module

  1. #1
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    Jan 2008
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    Hardy Heron (Ubuntu Development)

    Question the acpi_cpufreq module

    Hi everybody,

    how does the linux kernel cpu frequency scaling work? It seems to me it switches to lower power states quickly when nothing is going on and switches a lot to a higher power state when there are interrupt calls from eg the graphics driver. That's what I can deduce from y experience.

    I know for a fact that Windows uses cpu load to determine the power state and multiplier, which I see as better, it allows you to run eg desktop effects while staying in a lower power state, while in Linux (with my assumption), the CPU continually switches to the higher power states, thus running hotter.

    Is this correct, and if it is, is there a way to change cpu scaling to respect cpu load instead of interrupt calls, as to perhaps reduce responsiveness, but increase cpu time spent in lower power states?

    Thanks

  2. #2
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    Re: the acpi_cpufreq module

    Usually, the CPU has optimizations built into it that doesn't read from the BIOS. With this in scope, a CPU will go faster when it receives more electricity. One of the concepts of "over-clocking" involves either slightly raising the electricity value or the clock speed multiplier. (A single CPU core basically runs like an over-complicated clock with gadgets attached.) In almost all cases, you should avoid over-clocking. Some hardware vendors claim to support it, but remember that flirting with danger quickly translates to needing a purchase of computer parts.

    Linux in its native state can run 10 times more efficiently on some notebook computers. Some users have reported running a battery for 8 hours of continuous usage where it would only have lasted an hour or less under Vista. Results vary of course. The Remix version of Ubuntu may have a few extra settings enabled for power-saving, but I think the same can be done in the standard distribution.

    I haven't checked the XFCE version of Ubuntu yet, which is Xubuntu. I would assume that since XFCE has a performance advantage over other GUIs like Gnome and KDE in regards to its resource usage that it would consume less battery power, but it's only speculation.

  3. #3
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    Hardy Heron (Ubuntu Development)

    Re: the acpi_cpufreq module

    Thanks for the answer, but you're talking about something else. I want to know how the kernel decides which power state is used, not how they work.

  4. #4
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    Nov 2008
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    Re: the acpi_cpufreq module

    Quote Originally Posted by rubenvb View Post
    how does the linux kernel cpu frequency scaling work?
    Quote Originally Posted by rubenvb View Post
    I want to know how the kernel decides which power state is used, not how they work.
    My bad.

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