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    SubjectRe: [PATCH][2.5.32] CPU frequency and voltage scaling (0/4)
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    On Wed, 2002-08-28 at 20:49, Linus Torvalds wrote:
    > The point is that the _policy_ (not the end result) needs to be pushed
    > down to the kernel, so that the kernel can do the right thing with it.
    >
    > That policy can be updated in "real time" from user space, of course. But
    > the fact is that you cannot just set a frequency and leave it at that, it
    > doesn't work.

    If you look at the papers on the original ARM cpufreq code you'll see a
    case where very long granuality user driven policy is pretty much
    essential. The kernel sometimes does not have enough information.

    Take a trivial example. My CPU is 99% idle. Should you drop the clock
    speed right down. On a generic system yes, on a system which has to meet
    very tight real time deadlines quite possibly not. In fact some
    processors (eg the MediaGX) actually have hardware assists for speeding
    the CPU clock up for realtime interrupt processing paths.

    That argument ultimately boils down to "should the /proc interface to
    cpufreq" be a seperate module to the core cpu_freq code called by kernel
    policy engines like ACPI. The answer is obviously "yes" - /proc is just
    one of the policy engines.




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