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    SubjectRe: [Linux-ia64] Re: web page on O(1) scheduler

    On Thu, 29 May 2003, Mike Galbraith wrote:

    > [...] What makes more sense to me than the current implementation is to
    > rotate the entire peer queue when a thread expires... ie pull in the
    > head of the expired queue into the tail of the active queue at the same
    > time so you always have a player if one exists. (you'd have to select
    > queues based on used cpu time to make that work right though)

    we have tried all sorts of more complex yield() schemes before - they
    sucked for one or another workload. So in 2.5 i took the following path:
    make yield() _simple_ and effective, ie. expire the yielding task (push it
    down the runqueue roughly halfway, statistically) and dont try to be too
    smart doing it. All the real yield() users (mostly in the kernel) want it
    to be an efficient way to avoid livelocks. The old 2.4 yield
    implementation had the problem of enabling a ping-pong between two
    higher-prio yielding processes, until they use up their full timeslice.

    (we could do one more thing that still keeps the thing simple: we could
    re-set the yielding task's timeslice instead of the current 'keep the
    previous timeslice' logic.)

    OpenOffice used to use yield() as a legacy of 'green thread'
    implementation - where userspace threads needed to do periodic yield()s to
    get any sort of multitasking behavior.


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