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    SubjectRe: [PATCH] x86,sched: Fix sched_smt_power_savings totally broken
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    On 10 January 2012 15:32, Arjan van de Ven <arjan@linux.intel.com> wrote:
    > On 1/10/2012 1:18 AM, Ingo Molnar wrote:
    >>
    >> * Suresh Siddha <suresh.b.siddha@intel.com> wrote:
    >>
    >>> On Tue, 2012-01-10 at 00:58 -0500, Youquan Song wrote:
    >>>> Thanks Peter! Here is the patch.
    >>>
    >>> Youquan, As far as I know both the
    >>> sched_smt_power_savings/sched_mc_power_savings are broken for atleast an
    >>> year.
    >>
    >> We want a single knob, sched_power_savings - with the mc_ and
    >> smt_ ones still kept and aliased to sched_power_savings, for
    >> compatibility reasons.
    >>
    >> As Peter said, the other reasonable option is to have no knob at
    >> all and restart this code from scratch.
    >>
    >> The other thing we should do is to add sane defaults: to turn on
    >> sched_power_savings *AUTOMATICALLY* when a system is obviously
    >> battery driven and turn it off when the system is obviously AC
    >> driven. User-space can still implement policy and override the
    >> kernel's default, but there's absolutely no excuse to not offer
    >> this default ourselves.
    >
    > a very good default would be to keep all tasks on one package until half
    > the cores in the package are busy, and then start spreading out.
    >

    The choice of spreading or not tasks is clearly architecture or even
    platform dependent. Can't we get such optimal threshold information
    from architecture code ?

    > I suspect that'll be the 90% case coverage.
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