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    SubjectRe: [PATCH] Option to disable AMD C1E (allows dynticks to work)
    On Fri, 14 Dec 2007 17:35:13 -0500
    Chuck Ebbert <cebbert@redhat.com> wrote:

    > On 12/14/2007 05:17 AM, Andi Kleen wrote:
    > >> so do whatever is necessary to enable dynticks.
    > >
    > > dynticks' main purpose is to save power, but C1e saves more power.
    > > Disabling C1e for dynticks would be a fairly useless default
    > > trade off.
    > >
    >
    > What about machines where the BIOS has disabled C1e on CPU 0 but
    > left it enabled on CPU 1 ??

    Do you mean Linux should enable C1E on CPU 0 if it's detected on CPU 1?
    C3 + dynticks make up a better power saver than simply C1E, as far as I
    know. Higher C-states should be enabled on such CPUs, as AMD docs say
    firmware should either enable C1E or C2 & C3 (it must provide one of
    these mutually exclusive options). I take having C1E on the second CPU
    but not the first as an attempt on BIOS's part to provide higher
    C-states instead of the former. How broken is it, really?

    But maybe someone with access to such hardware can tell us what
    happens: does he get C2/C3 power states under such circumstances?


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