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    SubjectRe: [tip PATCH v7 0/9] RFC: futex: requeue pi implementation
    Thomas Gleixner wrote:
    > Darren,
    >
    > On Fri, 3 Apr 2009, Darren Hart wrote:
    >> The following series is v7 of the requeue_pi patches against
    >> linux-2.6-tip/core/futexes. The current futex implementation doesn't allow for
    >> requeueing of PI futexes, which leads to a thundering herd during
    >> pthread_cond_broadcasa()t (as opposed to a civilized priority ordered wakeup
    >> sequence). The core of the problem is that the underlying rt_mutex cannot be
    >> left with waiters and no owner (which would break the PI logic). This patch
    >> series updates the futex code to allow for requeueing from non-PI to PI futexes
    >> in support of PI aware pthread_cond_* calls along with some needful rt_mutex
    >> helper routines. The credit for the conceptual design goes to Thomas Gleixner,
    >> while the bugs and other idiocies present in this implementation should be
    >> attributed to me.
    >
    > I went through the patches with a fine comb again and there is nothing
    > left which triggered my futex wreckage sensors. Thanks for your
    > patience to go through the lather, rinse, repeat drill.
    >
    > I think we are at a point where that code simply needs exposure to the
    > hostile environment of RT-Java VMs. I'm going to pull that into
    > tip/next and into -rt. Even if we have no requeue_pi user right now we
    > definitly want to test the heck out of the changes which also affect
    > the existing futex ops.
    >
    > Uli, Jakub can you please go over the design and the user space
    > interface ?
    >
    > Darren, could you please polish the initial design notes - especially
    > point out the subtle differences between requeue and requeue_pi - and
    > send them into the thread? That might help Uli and Jakub and we
    > definitly want to have that info preserved in Documentation/ as well.
    >

    Thanks Thomas! I'll review and update the docs (the emails you sent me
    last year along with git commit messages for these patches) and send out
    a new requeue_pi design and implementation document that we can consider
    for inclusion in Documentation/. I'll try and have something out on Monday.

    --
    Darren Hart
    IBM Linux Technology Center
    Real-Time Linux Team


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