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    SubjectRe: [PATCH v2 0/2] cpu: pseries: Offline state framework.
    On Thu, 2009-09-24 at 18:38 +1000, Benjamin Herrenschmidt wrote:
    > On Thu, 2009-09-24 at 09:51 +0200, Peter Zijlstra wrote:
    > > > I don't quite follow your logic here. This is useful for more than just
    > > > hypervisors. For example, take the HV out of the picture for a moment
    > > > and imagine that the HW has the ability to offline CPU in various power
    > > > levels, with varying latencies to bring them back.
    > >
    > > cpu-hotplug is an utter slow path, anybody saying latency and hotplug in
    > > the same sentence doesn't seem to grasp either or both concepts.
    > Let's forget about latency then. Let's imagine I want to set a CPU
    > offline to save power, vs. setting it offline -and- opening the back
    > door of the machine to actually physically replace it :-)

    If the hardware is capable of physical hotplug, then surely powering the
    socket down saves most power and is the preferred mode?

    > In any case, I don't see the added feature as being problematic, and
    > not such a "layering violation" as you seem to imply it is. It's a
    > convenient way to atomically take the CPU out -and- convey some
    > information about the "intent" to the hypervisor, and I really fail
    > to see why you have so strong objections about it.

    Ignorance on my part probably :-)

    I'm simply not seeing a use case for it, except for the virt case, which
    I think we should bug the virt interface with and not the cpu-hotplug

     \ /
      Last update: 2009-09-24 13:35    [W:0.021 / U:67.436 seconds]
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