3/24/2023 0 Comments Enqueue time complexity![]() ![]() Enqueue operations in a binary heap are accomplished by inserting the new element at the bottom of the heap and performing compare-swap operation with successive parents until the priority of the new element is less than its parent. Queue operations are explained in detail below. The address decoder generates addresses and control signals for the BRAM blocks. Elements in each level of the heap are stored in separate on-chip memories called Block Rams (BRAMs) to enable parallel access to heap elements, similar to. Central to the priority queue is the queue manager, which provides the necessary interface and executes operations on the queue. A high level architecture diagram for the priority queue is shown in Figure 3. Although the dequeue operation takes O (log n ) time to complete, the top-priority task can be returned immediately, so that a dequeue operation overlaps its work with that of the rest of the scheduler and the application. Here we present a hardware implementation of the conventional binary heap that supports enqueue and peek operations in O (1) time and dequeue operations in O (log n ) time. Given an index i of an element, i / 2, 2 i and 2 i + 1 are the indices of its parent, left and right child respectively. The binary heap is stored as a linear array where the first element corresponds to the root. One of the common software data structures for implementing a priority queue is the binary heap, which supports enqueue and dequeue operations in O (log n ) time. At the core of the scheduler are the task queues, which are implemented as priority queues that keep the tasks in sorted order based on their priority (ready queue) or activation time (sleep queue). ![]() The task with the earliest activation time is at the front of the sleep queue. The sleep queue stores sleeping tasks until their activation time. The ready queue stores active tasks based on their priority. Basic scheduler operations such as run, configure, add task, and preempt task are supported. This removes bus dependencies for data transfer. The interface to the scheduler is provided through a set of custom instructions as an extension to the instruction set architecture of the processor. The resolution of the timer-tick can be configured at runtime. This provides accurate high-resolution timing for the scheduler. The timer unit keeps track of time elapsed since the start of the scheduler. The controller processes instruction calls from the processor and monitors task queues. It is responsible for the execution of the scheduling algorithm. The controller is the central processing unit of the scheduler. ![]() A high level block diagram of the hardware scheduler is shown in Figure 2. The check is accomplished using a single custom instruction that returns a preempt flag set by the hardware scheduler, based on which the processor can then choose to continue the execution of the current task or to run another. A software timer periodically generates interrupts to check for the availability of a higher priority task. The hardware scheduler executes the scheduling algorithm and returns the control to the processor along with the next task to execute, and context switching is then done in software. The instruction set architecture of the processor is correspondingly extended to support a set of custom instructions to communicate with the scheduler. The design also uses concurrency in hardware to make the operations on a priority queue more predictable. The hardware scheduler architecture we propose is designed to reduce time-tick processing and scheduling overhead of the system. The hardware utilization of the our priority queue increases logarithmically with the queue size and avoids complex pipelining logic. The hardware priority queue supports constant time enqueue operations and dequeue operations in O (log n ) time. The priority queue is used as a part of the scheduler to improve system performance and predictability. this paper we present a scalable hardware priority queue architecture that implements a conventional binary heap in hardware. ![]()
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