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    SubjectRe: [patch] Real-Time Preemption, plist fixes

    * Esben Nielsen <simlo@phys.au.dk> wrote:

    > Sorted lists works deterministicly O(1) on UP if no owner of the lock
    > blocks while having the lock. On SMP or worse if an owner blocks in
    > the lock, the wait list can grow very long. Thus insertion of new
    > elements takes a long time - with preemption disabled :-(

    the wait list can grow only as long as the max # of RT tasks is. Sorted
    lists become 'O(1)' if we added some code that globally limits the
    number of RT tasks to say 50. E.g. /proc/sys/kernel/max_nr_RT_tasks. A
    user can override it if he needs more RT tasks. There can be an
    arbitrary number of SCHED_OTHER tasks.

    (note that on Linux there is a RAM-dependent 'max # of tasks' ulimit
    which is never 'infinity', so theoretically the sorted lists are "O(1)"
    too. But this is nitpicking.)

    > If this is supposed to be used for user-space PI as well I would say
    > it would have to be completely bounded, i.e. plists are certainly
    > needed. [...]

    yes, it's supposed to be used for user-space PI too. What do you mean by
    'completely bounded'. Do you consider the current worst-case O(100)
    property of plists a 'completely bounded' solution?

    i dont think fusyn's should be made available to non-RT tasks. If this
    restriction is preserved then fusyn's would become O(max_nr_RT_tasks)
    too.

    Ingo
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