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    SubjectRe: [linux-pm] [PATCH] cpuidle: avoid singing capacitors
    On Wed, 12 Mar 2008 15:11:17 -0400
    Len Brown <lenb@kernel.org> wrote:

    > > I guess the only way to find out is to disassemble the DSDT. Exposing myself to such concentrations of ACPI is not an appealing project. :/
    >
    > the latest cpuidle code actually publishes the details of the C-states being used.
    >
    > $ pwd
    > /sys/devices/system/cpu/cpu0/cpuidle/state3
    > $ grep . *
    > desc:ACPI FFH INTEL MWAIT 0x20
    > latency:17
    > name:C3
    > power:250
    > time:1862590932
    > usage:9028970
    >
    > You'll see "desc" change if ACPI pulls a _CST change on you.
    >

    It does not. But my C3 desc looks like this:

    state3/desc:ACPI FFH INTEL MWAIT 0x50

    What's the meaning of the last number?

    I also have different latency and power:

    state3/latency:162
    state3/power:100

    > > Disabling the second core makes the noise go away. This might be a subset of 1., as I've been told that a stopped core enters C1.
    >
    > if you disable it at run-time, Linux puts it in C1.
    > If you never boot it in the first place (eg. maxcpusp=1), the BIOS leaves it in the deepest available C-sate.
    >

    Ah. Didn't know that. I've confirmed this as the noise is there when booting with maxcpus.

    > >
    > > So for now, the only viable workaround is processor.max_cstate....
    >
    > yup, that's why we put it in. Is it insufficient?
    >

    For some value of insufficient. It is sub-optimal. I'm hoping there is a way to enter C3 in a pattern that avoids the noise and still gives a reduced power usage.

    Rgds
    --
    -- Pierre Ossman

    Linux kernel, MMC maintainer http://www.kernel.org
    PulseAudio, core developer http://pulseaudio.org
    rdesktop, core developer http://www.rdesktop.org


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