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    SubjectRe: NPTL mutex and the scheduling priority
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    On Tue, 2006-06-13 at 04:48 -0400, Jakub Jelinek wrote:
    > On Mon, Jun 12, 2006 at 05:24:28PM +0200, S?bastien Dugu? wrote:
    > > The patch you refer to is at
    > > http://marc.theaimsgroup.com/?l=linux-kernel&m=114725326712391&w=2
    > >
    > > But maybe a better solution for condvars would be to implement
    > > something like a futex_requeue_pi() to handle the broadcast and
    > > only use PI futexes all along in glibc.
    >
    > FUTEX_REQUEUE certainly should be able to requeue from normal futex
    > to a PI futex or vice versa, I don't think it is desirable to create
    > a separate futex cmds for that.

    Indeed, that would be preferable but might get tricky.

    > Now not sure what do you mean by "use PI futexes all along in glibc",
    > certainly you don't mean using them for normal mutexes, right?
    > FUTEX_LOCK_PI has effects the normal futexes shouldn't have.
    > The condvars can be also used with PP mutexes and using PI for the cv
    > internal lock unconditionally wouldn't be the right thing either.

    I effectively meant using a PI futex for the cv __data.__futex but now
    I realize it's a Really Bad Idea.

    To summarize (correct me if I'm wrong), we need a way in the broadcast
    case to promote the cv __data.__futex type to the type of the external
    mutex (PI, PP, normal) in the requeue path. Therefore we need the
    ability to requeue waiters on a regular futex onto a PI futex.

    Ingo, Thomas, is this feasible?

    Sébastien.



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