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    SubjectRe: [PATCH 3/4] 2.6.2-rc2-mm2 CPU Hotplug: The Core

    On Tue, 3 Feb 2004, Rusty Russell wrote:

    > Wrong migration thread. The migration thread on CPU 1 has been asked to
    > push into CPU 0, which is now going down.

    you are right - this one place would have to be aware of CPUs going away.

    > Now I've slept on the "do it atomically" idea, I think it's a good one.
    > I've even worked out how to maintain the "last thread on CPU is the idle
    > thread", although I'd need to test in code.


    > In practice, any app which wants to scale with # CPUs needs to know when
    > CPUs are coming up, as well as going down. Ditto memory, etc. This
    > means they need to listen for the hotplug event (DBUS anyone?), or we
    > introduce a SIGRECONF (default ignored). But AFAICT, introducing a new
    > signal isn't possible (at least on x86) without breaking glibc.

    you can introduce a variable RT signal for this purpose no problem - and
    one would want to have a queued signal for this anyway. Ie. by default the
    notification is disabled, but a new syscall sets up the process to be
    notified of CPU up/down events, on a signal # picked by the app. But this
    this indeed is dbus domain ...

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