| 摘要 |
A prefetch buffer is used in connection with a plurality of independent thre ad processes in such a manner as to avoid an immediate stall when execution is given to an idle thread. A mechanism is established to control the switching from one thread to another within a Processor in order to achieve more efficient utilization of processor resources. This mechanism will grant temporary control to an alternate execution thread when a short latency even t is encountered, and will grant full control to an alternate execution thread when a long latency event is encountered. This thread control mechanism comprises a priority FIFO, which is configured such that its outputs control execution priority for two or more execution threads within a processor, based on the length of time each execution thread has been resident within the FIFO. The FIFO is loaded with an execution thread number each time a new task (a networking packet requiring classification and routing within a network) is dispatched for processing, where the execution thread number loaded into the FIFO corresponds to the thread number which is assigned to process the task. When a particular execution thread completes processing of a particular task, and enqueues the results for subsequent handling, the priority FIFO is further controlled toremove the corresponding execution thread number from the FIFO. When an active execution thread encounters a lo ng latency event, the corresponding thread number within the FIFO is removed from a high priority position in the FIFO, and placed into the lowest priority position of the FIFO. This thread control mechanism also comprises a Thread Control State Machine for each execution thread supported by the processor. The Thread Control State Machine further comprises four states. A n Init state is used while an execution thread is waiting for a task to process. Once a task is enqueued for processing, a Ready state is used to request execution cycles. Once access to the processor is granted, an Execute state is used to support actual processor execution. Requests for additional processor cycles are made from both the Ready state and the Execute state. The state machine is returned to the Init state once processing has been completed for the assigned task. A Wait state is used to suspend requests for execution cycles while the execution thread is stalled due to either a long-latency event or a short-latency event. This thread control mechanism further comprises an arbiter which uses thread numbers from the priority FIFO to determine which execution thread should be granted access to processor resources. The arbiter further process es requests for execution control from each execution thread, and selects one execution thre ad to be granted access to processor resources for each processor execution cycle by matching thread numbers from requesting execution threads with corresponding thread numbers in the priori ty FIFO.
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