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PIP and PCP

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      1 min de lecture

    • source

      llms.txt

    Priority Inheritance Protocol (PIP)

    idea: increase the priorities only upon resource contention

    avoid NPCS drawback

    would still run into deadlock (think of RR task resource access)

    rules:

    • When a task T1 is blocked due to non availability of a resource that it needs, the task T2 that holds the resource and consequently blocks T1, and T2 inherits the current priority of task T1.
    • T2 executes at the inherited priority until it releases R.
    • Upon the release of R, the priority of T2 returns to the priority that it held when it acquired the resource R

    Priority Ceiling Protocol (PCP)

    idea: extends PIP to prevent deadlocks

    • If lower priority task TL blocks a higher priority task TH, priority(TL) ← priority(TH)
    • When TL releases a resource, it returns to its normal priority if it doesn’t block any task. Or it returns to the highest priority of the tasks waiting for a resource held by TL
    • Transitive
      • T1 blocked by T2: priority(T2) ← priority(T1)
      • T2 blocked by T3: priority(T3) ← priority(T1)

    ceiling(R): highest priority. Each resource has fixed priority ceiling

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