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    SubjectRe: [Xen-devel] [PATCH 05/27] xen, cpu hotplug: Don't call cpu_bringup() in xen_play_dead()
    On 06/05/2012 11:10 PM, Thomas Gleixner wrote:

    > On Sat, 2 Jun 2012, Srivatsa S. Bhat wrote:
    >> Ok.. So, I would love to hear a confirmation about whether this patch (which
    >> removes cpu_bringup() in xen_play_dead()) will break things or it is good as is.
    >>
    >> If its not correct, then we can probably make __cpu_post_online() return an int,
    >> with the meaning:
    >>
    >> 0 => success, go ahead and call cpu_idle()
    >> non-zero => stop here, thanks for your services so far.. now leave the rest to me.
    >>
    >> So all other archs will return 0, Xen will return non-zero, and it will handle
    >> when to call cpu_idle() and when not to do so.
    >>
    >> Might sound a bit ugly, but I don't see much other option. Suggestions are
    >> appreciated!
    >
    > Yes, it's butt ugly.
    >
    > You are tripping over the main misconception of the current hotplug
    > code: It's asymetric.
    >
    > So people added warts and workarounds like the xen one. What you are
    > proposing is another wart and workaround.
    >
    > The real way to avoid it, is to have the symetric state machine in
    > place first and then convert everything to that instead of introducing
    > an intermediate state which resembles the existing state.
    >
    > One of the main things we need to do to make it symetric is to kill
    > the play_dead() thing in the idle loop and make idle a function which
    > returns on cpu_should_die().
    >
    > Give me a day or two and I get you a working version of that. (Up is
    > functional, just down refuses to play along)
    >


    Oh great! So, then I'll wait for your patches and then adapt this patchset
    to your model then. Let me know if I can help out with something..

    Regards,
    Srivatsa S. Bhat



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