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    SubjectRe: [PATCH] proposed scheduler enhancements and fixes
    Hi!

    > On 25 Feb 2000, Dimitris Michailidis wrote:
    > >
    > > * adds a new scheduling policy SCHED_IDLE. Processes of this type run on CPUs
    > > that would otherwise be idle. Useful for apps like SETI@Home, code crackers,
    > > etc. Implementation of this feature is extremely lightweight.
    > > Among the scheduling functions only schedule() is SCHED_IDLE-aware
    > > and the overhead for non-idle CPUs is at most 1 instruction per schedule()
    > > invocation;
    >
    > So why do you think your implementation of this doesn't have the deadlock
    > that every other implementation has?
    >
    > The deadlock is due to priority inversion, where a "idle-priority" task
    > gets a resource (say the directory semaphore), goes to sleep, and never
    > wakes up again because there is some slightly more important process
    > running all the time.
    >
    > In short, this has been tried before, and it has ALWAYS been a serious
    > security holw full of denial-of-service kind of attacks.

    No. Once upon a time, there was trick which enabled slow for
    SCHED_IDLE processes (by abusing flags -- something like PTRACE), then
    did priority boost in slow path. I even remember it made fast path
    slightly faster by assembly level optimalization.

    Unfortunately, that clever trick is not present in this sched patch.

    Pavel
    --
    I'm pavel@ucw.cz. "In my country we have almost anarchy and I don't care."
    Panos Katsaloulis describing me w.r.t. patents me at discuss@linmodems.org

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