Hybrid queue for storing instructions from fetch queue directly in out-of-order queue or temporarily in in-order queue until space is available

Abstract

A queuing apparatus having a hierarchy of queues, in one of a number of aspects, is configured to control backpressure between processors in a multiprocessor system. A fetch queue is coupled to an instruction cache and configured to store first instructions for a first processor and second instructions for a second processor in an order fetched from the instruction cache. An in-order queue is coupled to the fetch queue and configured to store the second instructions accepted from the fetch queue in response to a write indication. An out-of-order queue is coupled to the fetch queue and to the in-order queue and configured to store the second instructions accepted from the fetch queue in response to an indication that space is available in the out-of-order queue, wherein the second instructions may be accessed out-of-order with respect to other second instructions executing on different execution pipelines.