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    SubjectRe: current linux-2.6.git: cpusets completely broken
    2008/7/13 Linus Torvalds <>:
    > On Sun, 13 Jul 2008, Dmitry Adamushko wrote:
    >> try_to_wake_up() -> ... -> wake_idle() does not see "cpu_active_map".
    > You're right. I missed a couple places, because that migrate code not only
    > ends up using "cpu_is_offline()" instead of "!cpu_online()" (so my greps
    > all failed), and because it has those online checks in multiple places.
    > Grr.
    > So it would need to change a few other "cpu_is_offline()" calls to
    > "!cpu_active()" instead (in __migrate_task at a minimum).

    it should have checked the result of select_task_rq() in
    try_to_wake_up() or modify wake_idle() alternatively.

    And let me explain one last time why I opposed your 'cpu_active_map' approach.

    I do agree that there are likely ways to optimize the hotplug
    machinery but I have been focused on fixing bugs in a scope of the
    current framework trying to keep it intact with _minimal_ changes (as
    it's probably .26 material).

    The current way to synchronize with the load-balancer is to attach
    NULL domains to all sched-domains upon CPU_DOWN_PREPARE and rebuild
    sched-domains upon CPU_DOWN, effectively making the load-balancer
    'blind' (and this way it's workable indeed). Perhaps it's an overkill
    and something like being proposed by Miao or you should be
    considered/tried as an alternative.

    Even if we place "!cpu_active()" in all the load-balancer-related
    places (btw., we can also do it with !cpu_online() / cpu_offline() as
    Miao did with his initial patch) :

    (1) common_cpu_mem_hotplug_unplug() -> rebuild_sched_domain() is still
    called pretty "randomly" (breaking the aforementioned model). At the
    very least it's an overkill;

    (2) sched-domains are broken (at least while CPU_{UP,DOMS} ops. are in
    progress) and in this state they are still used in a number of places.
    That's just illogic;

    With (2) in place, "cpu_mask_active" acts as a workaround to the
    existing (broken by CPUSETS) model.
    If we want "cpu_mask_active" as a primary solution, then the current
    model should be altered (presumably, we don't need NULL domains any
    more). Otherwise, it's kind of a strange (illogical) hybrid.

    > Linus

    Best regards,
    Dmitry Adamushko

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