Direct parallel path for storage accesses unloading common system path

Abstract

A fast path (comprising control and data busses) directly connects between a storage element in a storage hierarchy and a requestor. The fast path (FP) is in parallel with the bus path normally provided through the storage hierarchy between the requestor and the storage element controller. The fast path may bypass intermediate levels in the storage hierarchy. The fast path is used at least for fetch requests from the requestor, since fetch requests have been found to comprise the majority of all storage access requests. System efficiency is significantly increased by using at least one fast path in a system to decrease the peak loads on the normal path. A requestor using the fast path makes each fetch request simultaneously to the fast path and to the normal path in a system controller element (SCE). The request through the fast path gets to the storage element before the same request through the SCE, but may be ignored by the storage element if it is busy. If accepted, the storage element can start its accessing controls sooner for a fast path request, than if the request is received from the normal path. Every request must use SCE controlled cross-interrogate (XI) and storage protect (SP) resources. Fast path request operation requires unique coordination among the XI and SP controls, the SCE priority controls, and by the storage element priority controls. When the accessed data is ready to be sent by the storage element, it can be sent to the requestor faster on the fast path data bus than on the SCE data bus. The fast path data bus may be used to transfer data for requests ignored from the fast path.