Cache coherence protocol with speculative writestream

Abstract

A system and method for performing speculative writestream transactions in a computing system. A computing system including a plurality of subsystems has a requesting subsystem configured to initiate a writestream ordered (WSO) transaction to perform a write operation to an entire coherency unit by conveying a WSO request to a home subsystem of the coherency unit. The requester is configured to perform the write operation without first receiving a copy of the coherency unit and complete WSO transactions initiated in the order in which they are initiated. The home subsystem is configured to process multiple WSO transactions directed to a given coherency unit in the order in which they are received. When the requester initiates a WSO transaction to a given coherency unit, the coherency unit is locked. Responsive to receiving the WSO request, the home subsystem conveys a pull request for the write data to the requester. If the requester detects a timeout condition, the requester may cancel the WSO transaction and unlock the coherency unit in the requesting node. The requester may further convey an acknowledgment to the home subsystem indicating no data will be returned. The home subsystem may then treat the WSO transaction as being complete.