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    SubjectRe: A few questions and issues with dynticks, NOHZ and powertop
    On Mon, Apr 05, 2010 at 09:23:16AM -0700, Arjan van de Ven wrote:
    > On 4/5/2010 9:22, Paul E. McKenney wrote:
    > >On Mon, Apr 05, 2010 at 09:07:33AM -0700, Arjan van de Ven wrote:
    > >>On 4/5/2010 8:14, Paul E. McKenney wrote:
    > >>>So the main issue is that for many workloads, it is best to run full bore
    > >>>and get done quickly, thus allowing the entire machine to be powered down?
    > >>
    > >>yep
    > >>
    > >>>If so, it seems likely that there would be some workloads that were sometimes
    > >>>unable to use all the CPUs, in which case shutting down (idling, offlining,
    > >>>dyntick-idling, whatever) the excess CPUs might nevertheless be the right
    > >>>thing to do.
    > >>
    > >>but the point is that the normal scheduler + idle behavior gives you exactly that
    > >>in a natural way !
    > >>If you don't have enough work (tasks) to keep all cores busy, the others are and stay idle.
    > >
    > >So your earlier objection was not to dyntick-idle as such, but rather
    > >to artificially constraining the scheduler to induce dyntick-idle?
    > my objection was against the notion that offlining cpus helps power/energy ;-)

    Fair enough, at least in general. I should hasten to add that Lai's
    patch also helps in the case where NR_CPUS is greater than the number
    of CPUs on the system.

    Thanx, Paul

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