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    SubjectRe: [RFC] cgroup TODOs

    On Fri, Sep 14, 2012 at 08:23:41PM +0200, Peter Zijlstra wrote:
    > Its hotplug, all hotplug stuff is synchronous, the last thing hotplug
    > needs is the added complexity of async callbacks. Also pushing stuff out
    > into worklets just to work around locking issues is vile.

    I was asking whether it *has* to be part of synchronous CPU hotplug
    operation. IOW, do all tasks in the depleted cgroup have to be moved
    to its parent before CPU hotunplug can proceed to completion or is it
    okay to happen afterwards? Making the migration part asynchronous
    doesn't add much complexity. The only thing you have to make sure is
    flushing the previously scheduled one from the next CPU_UP_PREPARE.

    Also note that this can't easily be solved by splitting tree
    protecting inner lock from the outer lock. We're talking about doing
    full migration operations which likely require the outer one too.

    > <handwave as I never can remember all the cgroup stuff/>
    > Can't we play games by pinning both cgroups with a reference and playing
    > games with threadgroup_change / task_lock for the individual tasks being
    > moved about?

    I'm lost. Can you please elaborate?



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