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Stack Resource Policy
The Stack Resource Policy (SRP) is a resource allocation policy used in real-time computing, used for accessing shared resources when using earliest deadline first scheduling. It was defined by T. P. Baker. SRP is not the same as the Priority ceiling protocol In real-time computing, the priority ceiling protocol is a synchronization protocol for shared resources to avoid unbounded priority inversion and mutual deadlock due to wrong nesting of critical sections. In this protocol each resource is assign ... which is for fixed priority tasks (FP). Function Each task is assigned a preemption level based upon the following formula where D(T_i) denotes the deadline of task i and \pi_i(T_i) denotes the preemption level of task i: D(T_i) \pi_i(T_j) Each resource R has a current ceiling C_R(V_R) that represents the maximum of the preemption levels of the tasks that may be blocked, when there are V units of R available and \mu_R(J) is the maximum units of R that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Earliest Deadline First Scheduling
Earliest deadline first (EDF) or least time to go is a dynamic priority scheduling algorithm used in real-time operating systems to place processes in a priority queue. Whenever a scheduling event occurs (task finishes, new task released, etc.) the queue will be searched for the process closest to its deadline. This process is the next to be scheduled for execution. EDF is an ''optimal'' scheduling algorithm on preemptive uniprocessors, in the following sense: if a collection of independent ''jobs,'' each characterized by an arrival time, an execution requirement and a deadline, can be scheduled (by any algorithm) in a way that ensures all the jobs complete by their deadline, the EDF will schedule this collection of jobs so they all complete by their deadline. With scheduling periodic processes that have deadlines equal to their periods, EDF has a utilization bound of 100%. Thus, the schedulability test for EDF is: :U = \sum_^ \frac \leq 1, where the \left\ are the worst-case com ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Priority Ceiling Protocol
In real-time computing, the priority ceiling protocol is a synchronization protocol for shared resources to avoid unbounded priority inversion and mutual deadlock due to wrong nesting of critical sections. In this protocol each resource is assigned a priority ceiling, which is a priority equal to the highest priority of any task which may lock the resource. The protocol works by temporarily raising the priorities of tasks in certain situations, thus it requires a scheduler that supports dynamic priority scheduling. ICPP versus OCPP There are two variants of the protocol: Original Ceiling Priority Protocol (OCPP) and Immediate Ceiling Priority Protocol (ICPP). The worst-case behaviour of the two ceiling schemes is identical from a scheduling view point. Both variants work by temporarily raising the priorities of tasks. In OCPP, a task X's priority is raised when a higher-priority task Y tries to acquire a resource that X has locked. The task's priority is then raised to the prio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
