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    SubjectRe: [PATCH 34/35] x86: use num_processors for possible cpus
    On 02/17/2010 06:38 PM, Yinghai Lu wrote:
    >>
    >> I'm confused by this one. This would seem to mean that unless you're
    >> specifying possible_cpus= then you are not treating anything as
    >> hotpluggable.
    >>
    >> This is clearly wrong, and it would appear to go the wrong direction in
    >> terms of what is safe.
    >>
    >> What am I missing here?
    >
    > per_cpu setup will allocate some mem for every cpu according to possible cpus.
    >

    Yes, and I have repeatedly requested that we allocate the memory on the
    first up of a disabled CPU rather than eagerly, but in *most*
    configurations the amount is relatively small.

    > no spec says that we should disable cpus entries in MADT as hotplug cpus.

    Reality seems to, though. Consider the bug report that led to patch
    681ee44d40d7c93b42118320e4620d07d8704fd6 for example.

    > also how many system that support hotplug cpus there?

    In terms of physical machines, not all that many; however, it is getting
    common to use CPU hotplug for virtual environments so they can be
    dynamically scaled.

    -hpa



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