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    SubjectRe: Status of X86_P4_CLOCKMOD?
    On Tue, Feb 28, 2006 at 01:46:29PM -0600, Matt Mackall wrote:
    > On Thu, Feb 23, 2006 at 03:41:10PM -0500, Dave Jones wrote:
    > > On Thu, Feb 23, 2006 at 08:59:37PM +0100, Adrian Bunk wrote:
    > >
    > > > > > > config X86_P4_CLOCKMOD
    > > > > > > depends on EMBEDDED
    > > > > >
    > > > > > This one is an x86_64 only issue, and yes, it's wrong.
    > > > >
    > > > > That's for P4, not X86_64... And since P4 clock modulation does not provide
    > > > > almost any energy savings it was "hidden" under embedded.
    > > >
    > > > But the EMBEDDED dependency is only on x86_64:
    > > >
    > > > arch/i386/kernel/cpu/cpufreq/Kconfig:
    > > > config X86_P4_CLOCKMOD
    > > > tristate "Intel Pentium 4 clock modulation"
    > > > select CPU_FREQ_TABLE
    > > > help
    > > >
    > > > arch/x86_64/kernel/cpufreq/Kconfig:
    > > > config X86_P4_CLOCKMOD
    > > > tristate "Intel Pentium 4 clock modulation"
    > > > depends on EMBEDDED
    > > > help
    > > >
    > > > And if the option is mostly useless, what is it good for?
    > >
    > > It's sometimes useful in cases where the target CPU doesn't have any better
    > > option (Speedstep/Powernow). The big misconception is that it
    > > somehow saves power & increases battery life. Not so.
    > > All it does is 'not do work so often'. The upside of this is
    > > that in some situations, we generate less heat this way.
    >
    > This is perplexing. Less heat equals less power usage according to the
    > laws of thermodynamics.

    you end up taking longer to do the same amount of work, so you
    end up using the same overall power.

    Dave
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